Solve Synchronization Problems in Outlook

When using Outlook, information is downloaded from the e-mail system and stored locally on your computer. Often there can be problems with synchronization with the e-mail server, for example, if there is a poor or slow network connection or if there are difficulties in saving on the computer. The error pattern can be very diverse. Possibly the contents of individual folders or even individual e-mails are no longer displayed in Outlook or there are problems with the use of calendars.

The following steps should help you to solve these problems. It is necessary that Outlook is already set up accordingly, you can find instructions on the following website:

Check for Outlook Problems

Before you perform the following actions to solve your problem, please check first, whether the observed problems are caused by Outlook (or Zimbra Connector for Outlook). To do this, access your personal mailbox via and check whether the problems can also be observed there. If this is the case, there is a general problem. In such a case, please contact the UCO (Tel: 5005, E-Mail: and describe the observed problem as precisely as possible.

If the problem can be observed in Outlook only, there is probably a problem in Outlook or Zimbra Connector for Outlook (ZCO) and the following measures should be checked step by step.

If you need assistance in performing the following steps, please contact the UCO (Tel: 5005, Email: uco@desy).

Parallel Operation of Outlook

It is not recommended to actively use Outlook on multiple devices at the same time, as experience has shown that this can lead to various synchronization problems and data inconsistencies. Therefore, if possible, try to work in a way that does not require parallel operation of Outlook and make sure to close Outlook after each use.

Offline Mode

In some cases, offline mode may be enabled in Outlook. This should usually be enabled so that synchronization of items from the mail server to your device can take place. You check if your Outlook is in offline mode as follows:

  1. Start Outlook
  2. In the menu, click on the tab "Send/Receive"
  3. If you see a button "Disable offline mode" in this menu, please click it to disable the offline mode

Afterwards observe the behavior in Outlook and see if it could be fixed this way.

Check Synchronizationintervall

If mails are displayed minutes later in Outlook than compared to Zimbra Web interface (, the synchronization frequency in Outlook could be a problem. In that case please check whether increasing the synchronizationintervall in Outlook brings any improvement:

  1. Start Outlook
  2. In the menu, click on the tab "Send/Receive" → "Send-Receive-Groups" → "Define Send-Receive-Groups"
  3. Set "Automatic delivery every ... minutes" to a smaller value, for example 5. This value should not be less than 3 (minutes)!

Afterwards observe the behavior for a few days and see if it could be fixed this way.


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Size of Mailbox

The size of the inbox can become problematic in Outlook if it exceeds 50GB. A size of no more than 20GB is recommended to be on the safe side. 50GB is a "hard" limit that is set by the Windows operating system and can only be changed with appropriate effort. Changing this limit is not recommended, as this may also cause unforeseen problems when using Outlook.

If necessary, you can check the size of your mailbox using the following method:

  1. Open the Control Panel → User Accounts → double click on Mail (Microsoft Outlook 2016)
  2. Select the Zimbra profile, click on 'Properties'
  3. Then select 'Data files ...' under Data files and enter your password.
  4. In the Data Files tab, click Open file location.
  5. Now check the size of the file on the right side



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Re-bind shared Objects

You can include e.g. e-mail folders of other accounts or calendars (e.g. seminar room calendars) in Outlook. It often helps to first remove the included elements and then add them again. To do this, proceed as follows.

If necessary, take some time, the newly included elements will then be resynchronized by Outlook, which can take a while depending on the size of the elements:

  1. Start Outlook
  2. Click on the "Zimbra" tab at the top of the menu and then click on "Share status"
  3. In the new window, uncheck the checkbox of an included item and then click "OK
  4. Repeat the third step until all check marks are removed.
  5. Exit Outlook and restart it
  6. Now use the same way to reattach all previously removed elements.
  7. Please wait until all elements are synchronized, you can see the progress clicking the button "Show Zimbra status"
  8. Only when all elements are synchronized again, please close Outlook again and restart it.

Afterwards observe the behavior and see if it could be fixed this way.

Please also note that you should only activate those elements that you actually use. Otherwise, above a certain amount, this can greatly slow down the entire operation of Outlook.

Location of the local Mailbox Files

Both your personal mailbox and bound calendars and inboxes are stored in separate files with the extension .zdb. The default location for these files is C:\Users\[account name]\AppData\Local\Microsoft\Outlook.

This location should not be changed under any circumstances. In particular, no network drive (H:\ or similar) should be used as a storage location. The reason for this is that connections to remote directories are usually slower than access to locally located files. Due to the permanently required access to the data files by Outlook, data inconsistencies cannot be excluded due to the possibly delayed reading and writing. That means that in worst case, data can be lost.

Therefore, please make sure in any case that you use a local storage location for your data files.

Re-create Outlook Profile

Only if none of the above mentioned ways helps, you may a new Outlook profile. The background here is that when you create a new Outlook profile, your personal inbox is completely resynchronized and all your view settings which you configured in Outlook will have to be reconfigured. The resynchronization normally takes a long time (depending on the size of your inbox). It is therefore advisable to initiate this either at the end of the working day or at least over the lunch break.

Instructions on how to set up a new Outlook profile can be found on the below mentioned website. Please note that the naming of the profile as "CreateZimbraProfile.exe" or "Zimbra" is mandatory in order not to be left out of centrally controlled changes that have to be performed by DESY-IT.