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IMAP connection to Exchange 2013 failed intermittently using Ms. Outlook

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  • IMAP connection to Exchange 2013 failed intermittently using Ms. Outlook

    Hi, we have migrated from Exchange 2003 (Windows Server 2003 R2) to Exchange 2013 (2 phase migration, now it's on Windows 2012 R2 with 2 domain controllers - Windows 2012 R2 as well with highest domain and forest functionality already) and everything working well (about a year) until now.

    We've experiencing a weird issue where access using IMAP (using Ms. Outlook on Windows and Mac - even with the latest version) failed intermittently (not always) especially from outside, the weird thing is it working well with other email client software (but due to some reasons we cannot force user to change their email client software hence we have to be able to fix the issue - said Big Boss ). We did a check using and test-imapconnectivity and everything working fine. Poking around for several days without any result, already tried reissue SSL certificate, changing port and encryption type, upgrade to latest patch - CU 12 (on CU 9 when this issue happened) and still no good result yet. Windows system is up-to-date (without .net 4.6).

    All ports are properly configured on Firewall for external access.
    All components are Active except ForwardSyncDaemon and ProvisioningRps however found if IMAP status is Unhealthy (log attached).

    Could anyone please advise how to solve the issue please....


    Attached Files

  • #2
    Finally...solved the issue:
    For anyone else experiencing the same issue, this is because since CU9 Microsoft introduced GSSAPI authentication protocol for Exchange server 2013. Before CU9, GSSAPI authentication protocol was not supported for POP3/IMAP clients in Exchange server 2013. Disable it and problem solved.