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jplace's avatar
jplace
Copper Contributor
Feb 09, 2024

Exchange On-Prem Messages Delayed Delivery to Exchange Online

We have an on-premises Exchange server (2019) which relays messages from on-premises clients (scanners, servers, etc.) and most of our user mailboxes are in Exchange Online.

 

Over the past few days, some (but not all) messages relayed from the on-premises server to exchange online get delayed for up to nearly 2 hours.  You can tell from the timestamps in the headers of the messages.

 

As an example, this morning, I ran the Get-Queue command on my on-premises server.  This showed 32 messages in the queue to my exchange online domain (myorg.mail.onmicrosoft.com).

Some of the messages had been delayed over an hour.

 

When I ran Get-Queue -Identity "8137"   nearly all the messages showed as being in "ready" status.

 

 

Nothing in queue was being delivered.

 

I then ran Retry-Queue -Identity "8137" and within about a minute all the messages were delivered.

 

As I noted, this has happened a few days in a row now and not sure why.  I've rebooted the server and it still persists, sometimes.

 

Can anyone suggest next steps to investigate why this is happening?

 

Exchange Online
Exchange Server
hybrid
  • Thomas_Koorts's avatar
    Thomas_Koorts
    Copper Contributor
    Feb 13, 2024

    Hijplace 

     

    1. Is your Exchange 2019 server also your hybrid server that relays emails between on-prem and EXO, or do you send to EXO externally?
    2. Is it a single on-premises server being used?
    3. Do you use anonymous relay on your on-prem receive connector for the scanners and servers?

     

    I would start with the following:

    1. Confirm that you have >10% free disk space on the C-drive to eliminate Exchange back pressure as an issue,
    2. Confirm that DNS is configured and working properly on your Exchange server, especially if you are using DNS round-robin for load-balancing,
    3. Assuming the 2019 Exchange server hosts the hybrid Send Connector, check other send connectors for possible conflicting config,
    4. Check that your hybrid servers' public IP is added to the Connection Filters in EXO,
    5. Check that your hybrid servers' public IP is not blacklisted.

    I also believe it is recommended that your accepted domain should be set to Internal Relay in a hybrid scenario, although I don't think that will delay delivery.

     

    Hope this helps.

     

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