delayed mail delivery

I have an Exchange 2016 DAG that communicates across a 10MBS ethernet the Primary server is located in a different building than the "Backup" and file witness share. Every once in a while some random users will experience a mail delay of up to 4 hours. This problem tends to "mysteriously" clear itself. I really doubt that the 10MBS ethernet configuration is the cause of the issue. I have experienced this issue myself and received the following NDR Remote Server returned '400 4.4.7 Message delayed' This issue happens internally as well as externally therefore I believe my issue to be an internal one.
Barry-f4Asked:
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SeanSystem EngineerCommented:
The most common issue is actually an issue with the receiving side. So if their exchange server is down or there is a DNS change that hasn't fully populated.
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Scott CSenior EngineerCommented:
Get the header of one of these delayed messages.  Run it through the message analyzer here.

https://testconnectivity.microsoft.com/

See where the message is being held.
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Barry-f4Author Commented:
This is an internal issue, the Exchange servers are all on line and as far as I know there have been no DNS changes
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timgreen7077Exchange EngineerCommented:
Get the header of one of the delayed emails (even though its internal), and that way you can see where the delay is happening during delivery from internal user to internal user. 10MBs is slow but unless you are sending a lot of emails you shouldn't have a 4 hour delay. The header needs to be one that was successfully delivered to the recipient (get the 4 hour one), not the sender.
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Barry-f4Author Commented:
I want to load the Exchange tool box on the primary server of my DAG. Is there any prep I should perform prior? Are there any pitfalls that i should be aware of ?
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timgreen7077Exchange EngineerCommented:
Nope, no worries its just tools.
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