I have used a registry fix to work on an IMAP issue of one of my client. The following error message I have found when I use Microsoft Remote Connectivity Analyzer

The certificate couldn’t be validated because SSL negotiation wasn’t successful

The fix:

Go to the following registry settings:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ExchangeServer\v15\ServerComponentStates\ImapProxy Functional

Change the existing value from 1:0:635797425487970123



Restart the IMAP windows services and you are done !


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  1. awpross

    After 20 hours of Problems, I found this Post, which helped me. I think the behaviour of IMAP and POP3 with Wildcard certificates have changed. This is why my Server, which I upgraded from a previous Version was working, and the new installed Servers had that Problem with wildcard certificate.
    Thank you very much.

  2. Stefan

    Thank you very much!
    Same problem with a new wildcard.
    After hours of searching I found your post and could fix it.
    Did the following:

    Set-ImapSettings -ExternalConnectionSettings “mail.XXXXX.XX:993:SSL”,”mail.XXXXX.XX:143:TLS” -X509CertificateName mail.XXXXX.XX
    Change the Reg. Value (1:0:63… to 1:1:63…)
    Restart-Service MSExchangeIMAP4; Restart-Service MSExchangeIMAP4BE


    • Good to hear that !

  3. tom

    Very recent post, after the April 2019 updates on my Exchange 2013 bent this setting.


    • Hope, the post helped you !


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