We have Exchange-based mail gate and Zimbra after that. Exchange receives mail from outer world and after AD checking relays all necessary mail to Zimbra.

For example.

client@outer.world -- > user@office.domain
All works fine, mail is delivered without errors.

The problem is:
When client@outer.world send mail with specific attach (unzipped MSOffice document) he receive NDR from Exchange and user@office.domain don't receive this letter in his inbox.

zmmsgtrace shows nothing about this letter. user@office.domain Inbox is working fine with no problems. Mail without attaches delivers fine.

Can't find errors in Exchange log files.

Any ideas?