Install instructions

WARNING: Beginning with release 3.0.0 .NET framework 4.6.1 is the minimal requirement.

Download and extract the OutlookCalDavSynchronizer-<Version>.zip into any directory and start setup.exe. You can change the default install path, but you need to use a directory on the C:\ drive. If the installer is complaining about the missing Visual Studio 2010 Tools for Office Runtime, install it manually from Microsoft Download Link You should also update manually to the latest Visual Studio 2010 Tools for Office Runtime (Version 10.0.60828) if you have an older version installed, since some COMExceptions have been fixed.

Beginning with version 2.9.0 the default install location is ProgramFilesDir\CalDavSynchronizer\ and the installer remembers the chosen directory for the next updates. Also the install option to install for Everyone instead of the current user is working now for Outlook 2010 and higher, if you want to install the addin for all users on the current machine. For Outlook 2007 you can only install the addin for the current user.

We recommend updating to the latest .Net Framework but the minimal required version is .NET 4.6.1, which is not supported on Windows XP. If you need Outlook CalDav Synchronizer for Windows XP you can download a backport to .Net 4.0 from a forked project here, thanks to Salvatore Isaja for the awesome work!

User Documentation


After installing the plugin, a new ribbon called ‚Caldav Synchronizer‘ is added in Outlook with 6 menu items. – Synchronize now – Synchronization Profiles – General Options – About – Reports – Status

For better accessibility the ribbon also supports keytips, accessible via ALT key followed by CDS and SN,SP,GO,AB,RE,ST respectively for the 6 items.

Use the Synchronization Profiles dialog to configure different synchronization profiles. Each profile is responsible for synchronizing one Outlook calendar/task or contact folder with a remote folder of a CalDAV/CardDAV server.

Beginning with version 2.15.0 advanced configuration settings are hidden by default and you can enable them by clicking on Show advanced settings and disable them again by clicking on Hide advanced settings. The default behaviour can also be configured as a general option, see below.

The toolbar on the left upper part provides the following options:

  • Add new profile adds a new empty profile
  • Add multiple profiles bulk profile creation to add multiple profiles at once and choose the folder for each discovered server resource (calendar, addressbook and task)
  • Delete selected profile deletes the current profile
  • Copy selected profile copies the current profile to a new one
  • Move selected profile up change ordering in the tree view (only in advanced settings)
  • Move selected profile down change ordering in the tree view (only in advanced settings)
  • Open data directory of selected profile Show directory with cached relations file in explorer for debugging (only in advanced settings)
  • Clear cache delete the sync cache and start a new initial sync with the next sync run.
  • Expand all nodes expand all nodes in the tree view, enabled by default but can be changed in general options (only in advanced settings)
  • Collapse all nodes collapse all nodes in the tree view (only in advanced settings)
  • Export Profiles to File and
  • Import Profiles from File See Profile Import/Export

When adding a new profile you can choose between a generic CalDAV/CardDAV, a google profile to simplify the google profile creation and predefined CalDAV/CardDAV profiles for SOGo, Fruux, Posteo, Yandex, GMX, Sarenet and Landmarks, Cozy Cloud, Nextcloud,, EasyProject, and SmarterMail where the DAV Url for autodiscovery is already entered.

The following properties need to be set for a new generic profile:

  • Profile name: An arbitrary name for the profile, which will be displayed in the tree view.
  • Outlook settings:
    • Outlook Folder: Outlook folder that should be used for synchronization. You can choose a calendar, contact or task folder. Depending on the folder type, the matching server resource type in the server settings must be used.
    • Synchronize items immediately after change Trigger a partial synchronization run immediately after an item is created, changed or deleted in Outlook (with a 10 seconds delay).
  • Server settings:
    • DAV Url: URL of the remote CalDAV or CardDAV server. You should use a HTTPS connection here for security reason! The Url must end with a /e.g.
    • If you only have a self signed certificate, add the self signed cert to the Local Computer Trusted Root Certification Authorities. You can import the cert by running the MMC as Administrator. If that fails, see section ‚Advanced options‘
    • Username: Username to connect to the CalDAV server
    • Password: Password used for the connection. The password will be saved encrypted in the option config file.
    • ** Use IMAP/POP3 Account Password** Instead of entering the password you can use the IMAP/Pop3 Password from the Outlook Account associated with the folder, the password is fetched from the Windows registry entry of the Outlook profile. (only in advanced settings)
    • ** Use WebDAV collection sync** WebDAV-Sync is a protocol extension that is defined in RFC 6578 and not supported by all servers. Test or discover settings will check if this is supported. This option can speed up the detection of server changes dramatically but excludes the possibility to use the time range filter. (only in advanced settings)
    • Email address: email address used as remote identity for the CalDAV server, necessary to synchronize the organizer. The email address can also be used for autodiscovery via DNS lookups, see section Autodiscovery.
    • Create DAV resource You can add server DAV resources (calendars or addressbooks). You can configure the resource displayname and if the url should be created with a random string or the displayname. For calendars you can also change the server calendar color. (only in advanced settings)
  • Sync settings:
    • Synchronization settings
      • Outlook -> Server (Replicate): syncronize everything from Outlook to the server (one way)
      • Outlook <- Server (Replicate): synchronize everything from the server to Outlook (one way)
      • Outlook -> Server (Merge): synchronize everything from Outlook to the server but don’t change events created on the server
      • Outlook <- Server (Merge): synchronize everything from the server to Outlook but don’t change events created in Outlook
      • Outlook <-> Server (Two-Way): Two-Way synchronization between Outlook and the server with one of the following conflict resolution
    • Conflict resolution (only used in Two-Way synchronization mode and only available in advanced settings)
      • Outlook Wins: If an event is modified in Outlook and in the server since last snyc, use the Outlook version. If an event is modified in Outlook and deleted in the server since last snyc, also use the Outlook version. If an event is deleted in Outlook and modified in the server, also delete it in the server.
      • Server Wins: If an event is modified in Outlook and in the server since last snyc, use the server version. If an event is modified in Outlook and deleted in the server since last snyc, also delete it in Outlook. If an event is deleted in Outlook and modified in the server, recreate it in Outlook.
      • Automatic: If event is modified in Outlook and in the server since last snyc, use the last recent modified version. If an event is modified in Outlook and deleted in the server since last snyc, delete it also in Outlook. If an event is deleted in Outlook and modified in the server, also delete it in the server
    • Synchronization interval (minutes): Choose the interval for synchronization in minutes, if ‚Manual only‘ is choosen, there is no automatic sync but you can use the ‚Synchronize now‘ menu item.
    • Perform synchronization in chunks and
    • Chunk size perform CalDAV/CardDAV sync in chunks with configurable chunk size to avoid OutOfMemoryEceptions, enabled by default because of lower memory consumption for huge resources. (only in advanced settings)
    • Use time range filter and
    • Synchronization timespan past (days) and
    • Synchronization timespan future (days) (only in advanced settings) For performance reasons it is useful to sync only a given timespan of a big calendar, especially past events are normally not necessary to sync after a given timespan. But be aware that Outlook and Google and some other CalDAV servers calculate the intersection with the time-range differently for recurring events which can cause doubled or deleted events, so it is recommended to select a time-range which is larger than the largest interval of your recurring events (e.g. 1 year for birthdays). You can’t use the time range filter together with WebDAV collection sync.
  • Is active checkbox in the tree view If deactivated, current profile is not synced anymore without the need to delete the profile.

If you expand the tree view of the profile you can configure network and proxy options and mapping configuration options. (only in advanced settings)

  • Network and proxy options: Here you can configure advanced network options and proxy settings.
    • Close connection after each request Don’t use KeepAlive for servers which don’t support it.
    • Use Preemptive Authentication Send Authentication header with each request to avoid 401 responses and resending the request, disable only if the server has problems with preemptive authentication.
    • Force basic authentication Set basic authentication headers to avoid problems with negotiation or digest authentication with servers like OS X. This is only recommended if you use a secure HTTPS connection, otherwise passwords are sent in cleartext.
    • Use System Default Proxy Use proxy settings from Internet Explorer or config file, uses default credentials if available for NTLM authentication.
    • Use manual proxy configuration Specify proxy URL as http://<your-proxy-domain>:<your-proxy-port> and optional Username and Password for Basic Authentication.
  • Mapping Configuration: Here you can configure what properties should be synced.
    • For appointments you can choose if you want to map reminders (just upcoming, all or none) and the description body.
    • Export html description X-ALT-DESC converted from RTF Body If enabled, convert formatted RTF Body of Outlook appointment to html and export it as X-ALT-DESC property. The RTF to html conversion is experimental, inline images and some formatting properties can’t be converted! Be aware that some servers like Google Calendar drop this attribute!
    • Set RTF Body from X-ALT-DESC html description If enabled, convert X-ALT-DESC description html property to RTF and set Outlook appointment RTF Body. The html to RTF conversion is experimental, not all html formatting options can be converted! This overwrites also the plaintext Body!
    • Timezone settings See section Timezone mapping below.
    • Use GlobalAppointmentID for UID attribute: Use Outlook GlobalAppointmendID instead of random Guid for UID attribute in new CalDAV events. This can avoid duplicate events from invitations.
    • In Privacy settings you can configure if you want to map Outlook private appointments to CLASS:CONFIDENTIAL and vice versa. This could be useful for Owncloud for example, if you share your calendar with others and they should see start/end dates of your private appointments. You can also map all CLASS:PUBLIC events to Outlook private appointments. And for Google calendar it is useful to map all Outlook public events to default visibility instead of PUBLIC.
    • In Scheduling settings you can configure if you want to map attendees and organizer and if notifications should be sent by the server.
    • Use *Don’t send appointment notifications for SOGo servers and SCHEDULE-AGENT=CLIENT for other servers if you want to send invitations from Outlook and avoid that the server sends invitations too, but be aware that not all servers (e.g. Google) support the SCHEDULE-AGENT=CLIENT setting.
    • In Outlook settings you can also define a filter category so that multiple CalDAV-Calendars can be synchronized into one Outlook calendar via the defined category (see Category Filter and Color below).
    • Cleanup duplicate events after each sync run: removes duplicate Outlook appointments based on start,end and subject of the events after each sync run, be aware of possible performance penalties with this option enabled.
    • For contacts you can configure if birthdays should be mapped or not. If birthdays are mapped, Outlook also creates an recurring appointment for every contact with a defined birthday. Similar, you can configure if anniversarys should be mapped or not.
    • You can also configure if contact photos should be mapped or not. Contact photo mapping from Outlook to the server doesn’t work in Outlook 2007. You can also add an option to not overwrite the contact photo in Outlook when it changes on the server, which could happen due to other mobile clients reducing the resolution for example.
    • Don’t overwrite FileAs in Outlook uses the Outlook settings for FileAs and doesn’t overwrite the contact FileAs with the FN from the server.
    • Fix imported phone number format adds round brackets to the area code of phone numbers, so that Outlook can show correct phone number details with country and area code, e.g. +1 23 45678 is mapped to +1 (23) 45678.
    • Map OutlookEmailAddress1 to WORK instead of HOME, enable when you need to change the order of email address mapping.
    • Write IM addresses as IMPP attributes. If enabled IMPP is used instead of X-AIM,X-ICQ,X-JABBER etc. for writing Instant messenger addresses in vCards.
    • Default IM protocol. Choose the default IM service type protocol which will be added to the chat address field from Outlook when writing vCards, defaults to AIM.
    • Map Distribution Lists enables the sync of contact groups / Distribution Lists, right now the DAV contact group format SOGo VLIST, vCards with KIND:group or iCloud groups are available, see Distribution Lists below.
    • For tasks (not for Google task profiles) you can configure if you want to map reminders (just upcoming, all or none), the priority of the task, the description body and if recurring tasks should be synchronized.
    • You can also define if task start and due dates should be mapped as floating without timezone to avoid issues with tasks across different timezones.
    • Similar to calendars you can also define a filter category so that multiple CalDAV Tasklists can be synchronized into one Outlook task folder via the defined category.

Timezone settings

Outlook and Windows use different Timezone definitions than most CalDAV servers and other clients. When adding new events on the server you have different options how the timezone of the newly created VEVENT is generated. The default setting uses the default Windows Timezone from Outlook (e.g. W. Europe Standard Time) or the selected timezones for the start and end of the appointment. Since some servers have problems with that timezone definitions you can change that behaviour in the event mapping configuration with the following options:

  • Create events on server in UTC Use UTC instead of Outlook Appointment Timezone for creating events on CalDAV server. Not recommended for general use, because recurrence exceptions over DST changes can’t be mapped and Appointments with different start and end timezones can’t be represented.
  • Create events on server in downloaded IANA Timezones Use Iana instead of Windows Timezones for creating events on CalDAV server. Needed for servers which do not accept non standard Windows Timezones like GMX for example. Timezone definitions will be downloaded from
  • Use IANA Timezone Use this IANA timezone for default Outlook/Windows timezone. Manually selected different timezones in Outlook appointments will be mapped to first corresponding IANA timezone.
  • Include full IANA zone with historical data Use full IANA timezone definition with historical data. Needs more bandwidth and can be incompatible when manually importing in Outlook.

Managing meetings and invites

Outlook can only track meeting responses and invites in the main calender folder. If you schedule meetings from Outlook which are synced with the CalDAV server you have two possibilities to avoid double invitation mails for all attendees. First, you can enable the option SCHEDULE-AGENT=CLIENT(or Don’t send appointment notifications (from SOGo)“ for SOGo servers) and let only Outlook send the meeting invites, if the server supports this option. Or you can disable this option and let the server schedule the meetings after syncing the meeting. Then you need to disable the invitation mails sent from Outlook. This is possible by unchecking the checkbox left to the attendee name in the meeting planning dialog. When syncing meetings created in Outlook to the server, the option Use GlobalAppointmentID for UID attribute is recommended. This can avoid duplicate events from invitations.

The response status of all attendees can be synced from Outlook to the server but only the status of the own Outlook identity (if included in the attendees) can be synced from the server to Outlook due to limitations of the Outlook Object Model.

When receiving invites from the CalDAV server and via Email in your INBOX, Outlook will automatically create a tentative meeting in the main calendar folder (This can be controlled with the Outlook Option ‚Automatically process meeting requests and responses to meeting requests and polls‘).

To avoid double meetings the option Cleanup duplicate events after each sync run in event mapping configuration is recommended.

Free/busy lookups

You can configure free/busy lookups globally in the outlook options. Select Options/Calendar and there free/busy information and use a free/busy url of your server with placeholder like %Name%, e.g. http://myserver/freebusy.php/%Name% Then every attendee in the outlook planning view gets resolved with that url for a free/busy lookup against your server.

Scheduling settings and resources

If your server supports resources (for SOGo see disable „set SCHEDULE-AGENT=CLIENT“ in Mapping Configuration, so that the server can handle the resource invitation mails, add the resource email adress as attendee in the Outlook appointment and choose type ressource (house icon) for it.

Category Filter and Color

If you want to sync multiple CalDAV calendars or tasklists into one Outlook folder you can configure an Outlook category for filtering in the Mapping Configuration. You can choose a category from the dropdown list of all available Outlook categories or enter a new category name. For all events/tasks from the server the defined category is added in Outlook, when syncing back from Outlook to the server only appointments/tasks with that category are considered but the filter category is removed. The category name must not contain any commas or semicolons! With the checkbox Sync also Appointments without any category also all appointments/tasks without a category are synced to the server. With the checkbox below you can alternatively negate the filter and sync all appointments/tasks except this category. For calendars it is also possible to choose the color of the category or to fetch the calendar color from the server and map it to the nearest supported Outlook category color with the button Fetch Color. With Set DAV Color it is also possible to sync the choosen category color back to set the server calendar color accordingly. With Category Shortcut Key you can define the shortcut key of the selected category for easier access when creating appointments.

Experimental mapping of the first category color of the appointment to the matching COLOR attribute of the event is also available with the option Map Event Color to Category. When mapping a COLOR from the server to Outlook the first matching Outlook category with that color is used, but mapping can be manually changed in the options.xml config file. Together with DAVdroid for Android you can map individual event colors from Android to Outlook,but not all calendar apps support it or can even crash, see


In event and task mapping configuration you can define if you want to map (all/non/just upcoming) reminders. If you get the following error message when trying to set reminders in Outlook

The reminder will not appear because the item is in a folder that doesn’t support reminders.

you can try to change the Outlook options as discussed in or try the following reported by #Todo18

  1. Create a new storage folder in Outlook via the File menu, Info, Account Settings. In the Data Files tab, you can Add a new (.pst) data file. After the file has been added, Make it the default [data file], and close the dialog.
  2. Go to the Calendar window, right click on the calendar that’s giving you problems, and select Move Calendar. In the dialog, pick the data file that you created in the first step, and confirm. Don’t forget to update the storage folder in the CalDav Synchronizer settings!

Custom properties mapping

When you expand the tree view of the profile for events and tasks, you can configure the mapping of custom properties.

  • Map all Outlook custom properties to X-CALDAVSYNCHRONIZER attributes If enabled, all Outlook custom text properties of the appointment/task are mapped to DAV attributes with the prefix X-CALDAVSYNCHRONIZER- and vice versa.
  • You can also define manual mapping pairs of Outlook custom attributes and DAV X-Attributes. This will overrule the general mapping of all Outlook custom properties if both is activated. Outlook properties that don’t exist, will be created. DAV properties MUST start with X-. Only Outlook custom properties of type Text can be mapped.

Distribution Lists

When enabled in Contact Mapping configuration you can now also sync Outlook Distribution Lists with your server contact groups. Since different servers use different formats to store contact groups, you will be able to choose the used DAV contact group format. Right now, the VLIST format for SOGo servers, vCards with KIND:group and iCloud groups are supported. Don’t enable any of these options when your server doesn’t support it!

Since Outlook Distribution Lists also support list members which aren’t in the addressbook but SOGo VLISTs don’t, we add them as custom X-Attributes. With this workaround those members aren’t displayed in SOGo but won’t get lost when syncing back to Outlook.

Since vCard in version 3.0 doesn’t support contact groups we use X-ADDRESSBOOK-SERVER attributes for KIND and MEMBER for contact groups and map the member CN and EMAIL for vCards with KIND:group or the member UID for the icloud groups.


When you are using an IMAP/POP3 Account with the same server settings (Username, Email address) you can press Get IMAP/POP3 account settings to discover those settings. The DAV url is discovered via DNS lookup from the account email address or the IMAP/POP3/SMTP server url if that fails. Together with the Use IMAP/POP3 account password checkbox activated you can fully autoconfigure the server settings from your existing account.

Instead of using the exact calendar/addressbook URL you can use the server address or the principal url and use the ‚Test or discover settings‘ button in the option dialog to try to autodiscover available calendars and addressbooks on the server. You can then choose one of the found calendars or addressbooks in the new window. If your server has redirections for well-known Urls (./well-known/caldav/ and ./well-known/carddav/ ) you need to enter the server name only (without path). If your domain configured DNS SRV and/or TXT lookups it is also possible leave the DAV url empty and discover it from the entered Email Address via DNS lookups, for example:

_carddavs._tcp 86400 IN SRV 10 20 443
_caldavs._tcp 86400 IN SRV 10 20 443

Proxy Settings

You can now set manual proxy settings in the Network and proxy options dialog in each profile. To override the default proxy settings from Windows Internet Explorer you can also specify settings in the app config file, see config options below. More information can be found at

General Options and SSL settings

In the General Options Dialog you can change settings which are used for all synchronization profiles.

  • Generel Settings
    • Automatically check for newer versions set to false to disable checking for updates.
    • Check Internet connection before sync run checks if an interface is up and try DNS query to first and if that fails try to download with the configured proxy before each sync run to avoid error reports if network is unavailable after hibernate for example. Disable this option if you are in a local network where DNS and that URL is blocked.
    • Include custom message classes in Outlook filter Disabled by default, enable only if you have custom forms with message_classes other than the default IPM.Appointment/Contact/Task. For better performance, Windows Search Service shouldn’t be deactivated if this option is enabled.
    • Use fast queries for Outlook folders Enabled by default, uses fast GetTable queries when accessing Outlook folders. Disable only if you get errors in GetVersions, when disabled every item needs to be requested which causes a performance penalty!
    • Trigger sync after Outlook Send/Receive and on Startup If checked a manual sync is triggered after the Outlook Send/Receive finishes and on Outlook startup.
    • Store data in roaming folder set to true if you need to store state and profile data in the AppData\Roaming\ directory for roaming profiles in a AD domain for example. When changing this option, a restart of Outlook is required.
  • UI Settings
    • Show advanced settings as default Show the advanced settings in synchronization profiles as default if enabled.
    • Expand all nodes in Synchronization profiles Enabled by default, expands all nodes in the synchronization profiles to see the suboptions for network settings and mapping configuration.
    • Enable Tray Icon Enabled by default, you can disable the tray icon in the Windows Taskbar if you don’t need it.
    • Fix invalid settings Fixes invalid settings automatically, when synchronization profiles are edited.
    • Show Sync Progress Bar and Sync Progress Bar Threshold (Items) Enabled by default, show a progress bar if more than the treshold of items need to be loaded during a synchronization run. If disabled, no progress bar is shown but be aware that for larger changes Outlook can freeze, since some operations need to be performed in the Outlook main thread.
    • Language Select UI language. When changing this option, a restart of Outlook is required.
  • Server Settings
    • Accept invalid chars in server response If checked invalid characters in XML server responses are allowed. A typical invalid char, sent by some servers is Form feed (0x0C).
    • ** Enable useUnsafeHeaderParsing** Enable, if the server sends invalid http headers, see common network errors. Needed for Yahoo and cPanel Horde servers for example. The general option overrides the setting in the app.config file.
    • CalDav Connection Timeout (secs) For slow server connections you can increaste the timeout value (default 90 secs).
  • SSL/TLS Settings
    • If you have problems with SSL/TLS and self-signed certificates, you can change the following settings at your own risk. The recommended way would be to add the self signed cert to the Local Computer Trusted Root Certification Authorities. You can import the cert by running the MMC as Administrator.
    • Disable Certificate Validation set to true to disable SSL/TLS certificate validation, major security risk, use with caution!
    • Enable Client Certificates If enabled, the available client certificates from the Windows user certificate store will automatically be provided.
    • Enable Tls12 set to false to disable TLS12, not recommended
    • Enable Ssl3 set to true to enable deprecated SSLv3, major security risk, use with caution!
  • Synchronization Reports
    • See Reports of sync runs below.
  • General Logging
    • In the General Logging section you can show or clear the log file and define the log level. Possible log levels are INFO and DEBUG.

Profile Import/Export

In the toolbar of the synchronization profiles you can export all profiles to a file and import profiles from an earlier exported file. When exporting, you can choose a filename, the extension is *.cdsp and all options are saved in an xml format into this file. When importing the file, existing profiles are merged with the imported ones. If the selected Outlook folder for the profile doesn’t exist during import, you need to manually select a folder before you can save the options, they are not automatically created. You need also be aware of the fact, that saved profile passwords won’t work on other accounts or machines, since the encryption is dependant on the current user. But you can use the account password from the IMAP/POP3 account if available. General options are not saved in that file, but in the registry in HKEY_CURRENT_USER\Software\CalDavSynchronizer.

Reports of sync runs

You can also configure Synchronization reports for all profiles, this can be configured via general Options:

  • Log You can choose if you want to generate reports for „Only sync runs with errors“ or „Sync runs with errors or warnings“ or „All sync runs“.
  • Show immediately configures if the Sync reports should be shown immediately after a sync run with errors, with warnings or errors, or not at all.
  • Delete reports older than (days) Automatically delete reports which are older than the days configured.
  • Log Entity Names Enable to display the summary of the event or task or the name of the contact to identify the entity in the sync report.
  • Log all entities, even without warnings or errors Enable if a full report of all modified entities is needed.

You can show reports manually with the Reports button in the CalDav Synchronizer Ribbon. There you can choose from available reports (shown as profile name with timestamp of the sync run) and see informations about items synced and if there were any warnings or errors. You can also delete reports or add them to a zip file via the context menu. If the last sync run lead to any errors, a warning symbol is shown in the Ribbon or the Report window opens if configured in the general options.

Synchronization Status and System TrayIcon with Notifications

With the Status button in the CalDav Synchronizer Ribbon or via doubleclick from the TrayIcon you can access the status of the active sync profiles with their last sync run shown in minutes ago and the status OK, error, or warning. When clicking on the profile name you get to the according sync profile settings, when clicking the status icon, you can open the according sync report. When a sync run has any errors or warnings you will get a notification from the CalDav Synchronizer TrayIcon.


Provider specific settings

Google Calender / Addressbooks / Tasks settings

For Google you can use the new Google type profile which simplifies the setup. You just need to enter the email address of your google account. When testing the settings, you will be redirected to your browser to enter your Google Account password and grant access rights to your Google Calender, Contacts and Tasks for OutlookCalDavSynchronizer via the safe OAuth protocol. After that Autodiscovery will try to find available calendar, addressbook and task resources.

You can control which calendars are available via CalDAV and shown in autodiscovery in your calendar settings, see

For contacts you should activate the checkbox Use Google native API. This will improve performance and other mapping issues, since the Google Contacts API supports more features than the generic CardDAV API. Compared to CardDAV this adds:

  • Support for google contact groups, which are synced to Outlook categories.
  • Added mapping for anniversary, relations (spouse, child, etc.) and IMs for google contacts (Contribution from Florian Saller, thank you!).

When switching between native API and CardDAV the sync cache is cleared and a complete initial sync is performed during next sync run.

For tasks you can choose the tasklist you want to sync with an Outlook task folder and the id of the task list is shown in the Discovered Url. With the button ‚Edit Url‘ you still can manually change the Url e.g. when you want to sync a shared google calendar from another account.

If you get an error with insufficient access you need to refresh the token by deleting the previous token inC:\Users\<your Username>\AppData\Roaming\Google.Apis.Auth

GMX calendar settings

For GMX calendar use the GMX Calendar account type, which sets the autodiscovery DAV Url Since GMX doesn’t allow to create events with the Windows Timezone IDs, for the GMX account type the Create events on server with downloaded IANA Timezones checkbox in Mapping Configuration is checked by default to avoid errors when creating events and syncing from Outlook to GMX.

For GMX addressbook use the DAV Url

Synology NAS settings

When test settings for your synology NAS profile, you can ignore the warning „The specified Url does not support calendar queries. Some features like time range filter may not work!“. But a user reported, that „Disable directory browsing“ setting must not be enabled for the calendar folder for proper syncing.

For Synology NAS with SSL support use port 5006 and the following settings in your NAS: In Synology DSM Navigate to control panel > Terminal & SNMP Select Enable SSH Then enter Advanced Settings and set it to High Now it will work on port 5006 with https.

iCloud settings

Apple changed their security policy recently (June 2017). You need to enable Two-Factor-Authentication and an app-specific password for CalDavSynchronizer, see

For syncing iCloud Calendar select the preconfigured iCloud Calendar profile type, which uses the following CalDAV URL

Only as a fallback if the autodiscovery fails you can use the following procedur To find the correct DAV url for iCloud you need some information from the MacOS, where you are connected with your calendar.

Open with Textedit: ~/Library/Calendars/*.caldav/Info.plist (Its in the hidden User-Library)

Check iCloud Path: PrincipalURL <string>https://p***********/principal/</string>

Check: DefaultCalendarPath <string>/*********/calendars/********-****-****-****-************</string>

Then you get the DAV url of the calendar: https://p***********/calendars/********-****-****-****-************/

For syncing iCloud contacts select the preconfigured iCloud contacts profile type, which uses the following CardDAV URL

and press ‚Test or discover settings‚ for autodiscovery, the final URL should look like<YOUR UNIQUE Apple USER_ID>/carddavhome/card/

There are PHP files available to determine your Apple USER_ID, see settings

The caldav server has problems with escaping, so if your calendar url looks something like

use the url


Trouble Shooting

Options and state information is normally stored in the following folder:

C:\Users\<Your Username>\AppData\Local\CalDavSychronizer

If you activated Store data in roaming folder the location is changed to the following folder:

C:\Users\<Your Username>\AppData\Roaming\CalDavSychronizer

There is one options_<your outlook profile>.xml file which stores the options for each outlook profile. For each sync profile there is a subfolder with state information stored in a relations.xml file after the inital sync. If you delete that folder, a fresh inital sync is performed. In the Synchronization profiles dialog a context menu is available in each profile (right click), which allows to open the cache directory and read the relations.xml file.

Each synchronization attempt is logged in the log.txt file. There you can find information about sync duration and the amount of added, deleted or modified events. Errors and Exceptions are logged aswell. You can view and clear the log file in General Options. There you can also change the log level from INFO to DEBUG.

Debugging and more config options

In the install dir (The default is 'C:\Program Files (x86)\CalDavSynchronizer') you will find the app config file


In that xml file you can config timeout parameters and config options in the section appSettings After changing parameters you have to restart Outlook.

  • wpfRenderModeSoftwareOnly: When set to true, turn off hardware acceleration and use Software Rendering only. Useful if you have issues with WPF and your graphics card driver.

You can also change defaults for some of the general options like CheckForNewVersions, StoreAppDatainRoamingFolder, IncludeCustomMessageClasses and SSL/TLS options, useful for All Users deployment, because general options are stored per user in the HKCU registry hive.

In the section you can define proxy settings, e.g. use of NTLM credentials

<defaultProxy useDefaultCredentials="true">

In this section you can also allow UnsafeHeaderParsing if the server sends invalid http headers.

        <servicePointManager expect100Continue="false" />
        <httpWebRequest useUnsafeHeaderParsing="true" />

This setting can also be enabled in the general options, starting with version 2.10.0.

In the section log4net you can define the log level for the main log (also possible in general options now) and for the caldav data access, level value can be DEBUG or INFO, e.g. :

  <level value="DEBUG" />
  <appender-ref ref="MainLogAppender" />

Common network errors

  • System.Net.Http.HttpRequestException: Response status code does not indicate success: ‚401‘ (‚Unauthorized‘).
    • Wrong Username and/or Password provided.
  • System.Net.Http.HttpRequestException: An error occurred while sending the request. —> System.Net.WebException: The underlying connection was closed: A connection that was expected to be kept alive was closed by the server.
    • The server has KeepAlive disabled. Use „Close connection after each request“ in Network and proxy options.
  • System.Net.Http.HttpRequestException: An error occurred while sending the request. —> System.Net.WebException: The server committed a protocol violation. Section=ResponseStatusLine
    • The server sends invalid headers. Enable the general option Enable useUnsafeHeaderParsing or the commented out option useUnsafeHeaderparsing in the app config file, see Debugging and more config options above.