EMWMSA.log contains the following entries:
"CMBRedir::MakeRedirector Error -520093684 Error 0xe100000c. 0xe100000c; 0x1;
1/24/2006 12:53:54 PM CMBMSwitcher::Switch Informational 4902 Cannot switch mailbox '/O=XXX/OU=XXX/cn=Recipients/cn=username'."
"Targetaddress" attribute for the account in source or proxy SMTP address in target domain cannot be set.
Mail Synchronization Agent (MSA) checks for the so-called redirector, the proxy SMTP address which has been created by the Directory Synchronization Agent (DSA) so the mail from the source could be delivered to the target mailbox. The address is created based on the template which was specified under "Specify Exchange Options" settings of the synchronization job.
The pattern for generating redirection addresses is as follows:
[Target_objects_primary_SMTP_address_prefix]@Source_SMTP_address_Template (specified in the properties of the Directory Synchronization Job)]
This check cannot not be completed successfully because such an address already exists within the proxy addresses in the Target AD and has to be removed or modified so the problematic mailbox could be switched successfully.
The same problem will arise when the MSA during the switching process tries to set the Target address of the source account to be the target users proxy address and an already existing SMTP address in source has been discovered.
When migrating from an environment with different Source domains, it often happens that some of the users have the same names (the left side of the primary smtp is what is used when checking names).
If there are several different sites that are being merged into one Target site then manually modify the target SMTP address. This will allow to switch the mailbox.
Search the proxy addresses for all objects in the entire target forest by connecting to the Root Domain Global Catalog on port 3268 and using ldp.exe utility to search within proxy addresses. After the object with duplicated address is found, delete or modify the address from the proxy addresses of the object and resynchronize the mail and calendar collection.
For information on another issue when migrating from multiple Source Domains refer to KB article 14420 - "Error when migrating users: "Error 0xe3000005. Target object matched by the following high-priority matching rule.":