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Slow Email Delivery (both internal and External) Exchange 2016 on-premise

Question
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Hi,
We have an on-premise Exchange 2016 Servers. Just recently we've had a user complain that SOME emails (a mixture of internal and external) are taking a long time to arrive.
i.e an internal email sent @ 12:21am was received @ 12:36am, another was sent at 6:32am and received at 6:41am and another was sent at 6:34am and received at 6:41am.Here are the HEADERS of one email
Received: from XXXXXXXEX01.XXXXXXX.XXX (XXX.XXX.XXX.XXX) by
XXXXXXXEX01.XXXXXXX.XXX (XXX.XXX.XXX.XXX)with Microsoft SMTP Server
(version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1713.5
via Mailbox Transport; Wed, 19 Jun 2019 06:41:21 +1000
Received: from XXXXXXXEX01.XXXXXXX.XXX (XXX.XXX.XXX.XXX)by
XXXXXXXEX01.XXXXXXX.XXX (XXX.XXX.XXX.XXX)with Microsoft SMTP Server
(version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id
15.1.1713.5; Wed, 19 Jun 2019 06:34:06 +1000
Received: from XXXXXXXEX01.XXXXXXX.XXX (XXX.XXX.XXX.XXX) ([XXXX::XXXX:XXXX:XXXX:XXXX]) by
XXXXXXXEX01.XXXXXXX.XXX (XXX.XXX.XXX.XXX) ([XXXX::XXXX:XXXX:XXXX:XXXX]) with mapi id
15.01.1713.004; Wed, 19 Jun 2019 06:34:06 +1000
Content-Type: application/ms-tnef; name="winmail.dat"
Content-Transfer-Encoding: binary
Any help or advise would be appreciated.
Thanks
All replies
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Hi TheWanKing,
Did you change anything on the server recently ? Is there only one user have the delay issue ?
You can try to check the message tracking log on these specific delayed messages , that would show us the details about where and when the message delay:
Moreover, you can also try using message analyzer in EXRCA to help analyze the message header, this tool will analyze the email’s path and, based on the timestamps when it passed the different machines, it will tell you the exact source that is responsible for delaying the message delivery.
Best Regards,
Niko Cheng
Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.
Click here to learn more. Visit the dedicated forum to share, explore and talk to experts about Microsoft Teams.- Proposed as answer by Niko.ChengMicrosoft contingent staff, Moderator Thursday, June 27, 2019 7:41 AM
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Hi,
Havent made any changes. In this case we've had a different user with the same issue. This is what i got from the Exchange Delivery REport. As you can see there's a 14 minute delay
We noticed the time it happened mail was queuing on this server
Delivery Report for USERXXXXX (USERXXXX@COMPANYXXXXXX.com)
Pending
1/07/2019 12:22 PM serverex01.internalname.com
Message was received by serverex01.internalname.com from serverex02.internalname.com.
1/07/2019 12:36 PM serverex01.internalname.com
The message has been transferred from serverex01.internalname.com to serverex01.internalname.com.
Delivered
1/07/2019 12:36 PM serverex01.internalname.com
The message was successfully delivered.- Edited by TheWanKing Monday, July 1, 2019 3:03 AM
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Hi TheWanKing,
How about the result after changing the MaxInboundConnectionPerSource value? If you have any questions or needed further help on this issue, please feel free to post back. If the issue has been resolved, please mark the helpful replies as answers, this will make answer searching in the forum easier and be beneficial to other community members as well.
Thanks for your understanding.Best Regards,
Niko Cheng
Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.
Click here to learn more. Visit the dedicated forum to share, explore and talk to experts about Microsoft Teams.- Edited by Niko.ChengMicrosoft contingent staff, Moderator Wednesday, July 3, 2019 9:38 AM