Already switched mailboxes are missing data in target mailbox; possible reasons and workarounds (4352444)

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Title

Already switched mailboxes are missing data in target mailbox; possible reasons and workarounds
Description

Mailbox has been switched but in target mailbox there are some items missing?

Why did the tool switch the not fully synchronized mailbox?

What can be done to resolve this problem?
Cause

Mail synchronization is being performed by 3 agents - the Mail Source Agent (MSA), the Mail Transmission Agent (NTA) and the Mail Target Agent (MTA).
The MSA logs on to the source mailbox and retrieves the data. The retrieved data (PRV file) is compressed and passed to the NTA for further processing. The NTA moves the PRV file to the target Exchange server. The MTA receives the PRV files, uncompress the file and delivers the file to the destination mailbox.
The agents don't communicate with each other.
When the MSA retrieves all the data from the source mailbox it performs the switching operation, it does not communicate with the MTA to check that all the data has been successfully processed, therefore it will switch the mailbox if allowed to do so (if configured accordingly).
If there have been issues such as:
- the NTA was not started or could not move files due to name resolution or connectivity issues;
- or the MTA was not able to deliver the data, eg. due to missing or incorrect permissions and not being able to logon to target mailbox;
Then target mailbox will be missing data. Theoretically a mailbox can be switched without an existing target mailbox or with an empty target mailbox.
Often there are some issues at the beginning of a migration (incorrect permission, native Exchange issues) and when these issues have been resolved and mail starts flowing it is already too late. The MTA was trying to delivers some data and since it was not able to deliver the data it archived the files, now they are marked as dead and will not be delivered.
Resolution

Knowing how it works one should always:

1. Observe the agents log files for possible errors or issues;

2. Use the Service File Viewer and watch the queue,observe that the files are being processed; and

3. Watch the ARCHIVE folder and be alarmed if at least one file gets archived, this means agent was not able to deliver the file

How to resolve:

Instead of attempting to re-process the archived (marked as dead) files one should perform a full resynchronization of the mailbox.

If a mailbox is already switched and target mailbox is missing items then this mailbox can be safely re-synchronized again.

The Support KB contains numerous articles with explanation how to resynchronize a single mailbox, how to resynchronize an already switched mailbox, how to resynchronize hierarchy (folder structure) and permissions only, how to use Service File Viewer, how to watch the logs live, etc.

Note: In most migrations administrators prefer this approach: they create as minimum of 2 collections and give them corresponding names, e.g. SYNC and SWITCH.

SYNC collection doesn't allow automatic switching. Once the mailbox has been fully synchronized and this has been verified and confirmed, admins move this mailbox to SWITCH collection, which allows automatic switching. One mailbox cannot be present in 2 collections at once. This is by design, so there is no need to remove the mailbox from SYNC collection, just adding to SWITCH collection will suffice.

Switching mailboxes manually is another alternative and could be brought into consideration, but it is recommended to use this feature only after it has been confirmed that target mailbox has been fully synchronized. For more details please see QMM Best Practices.
Additional Information

It is a good idea to use the Statistics Portal and switch mailboxes only when the amount of items (NOT THE SIZE) matches in source and in target.

Alternatively another tool can be used, e.g. Quest has a product called MessageStats. To obtain this product please contact your Quest Account Manager.

Professional Services also have a script available which will compare the source and target mailboxes. Support doesnt have this script and cannot provide any assistance when using this script, but it is a very interesting option and if interested in obtaining and using such a script please contact your Quest Account Manager

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Already switched mailboxes are missing data in target mailbox; possible reasons and workarounds (4352444)

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