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FuriousHaggis's avatar
FuriousHaggis
Copper Contributor
Jul 20, 2023
Solved

Mail Queuing and not being delivered on Ex2016 to EXO

Hello. I have an issue with mail building up in our Ex2016 queues. This transports from our 3rd party gateway to Exchange online as part of a hybrid setup. Our mailboxes are all in EXO. Restarting th...
2016
exchange online
Exchange Server
hybrid
FuriousHaggis's avatar
FuriousHaggis
Copper Contributor
Jul 25, 2023
ANSWER: Firewall was blocking connection from Onprem to EXO which was resolving to an IP block we've not seen before. Adding this to the FW rule resolved. I found 451 4.4.397 errors in the SMTP logs to get me there. The IP block was in MS's documentation so was either missed when we set up or added afterwards.
  • Dan_Snape's avatar
    Dan_Snape
    Steel Contributor
    Jul 27, 2023

    FuriousHaggisIt's always the network :lol:

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