I posted the following question about email delays, which I was able to answer myself (together with my client's great help). My post was deleted but I wanted to post again because I have an answer that could help.
POST: Hello, I am a new Office 365 user and am experiencing 11 hour email delays from my best client. I have to get this fixed right away. The delay seems to relate only to this client's domain name (emails from all users at that domain are being delayed on their way to me). How do I get this fixed? Thank you
ANSWER: I wanted to close the loop on this delayed email issue with some forensic analysis of the problem (which is now fixed, though we are not sure how or why what was done fixed the problem or where the “true” problem was). Here is what my client determined (they use 2003 MS Exchange server). I am a non-techy, but here is my summary:
1) They moved a microsoft DNS server up higher in their list of dns servers and this “fixed” the problem. Apparently, emails were going through their first or 2nd outgoing dns servers, were not able to connect to MS 365 bigfish server, then waited to resend. The sending server waited say 2-3 hours before it tried to resend and eventually found a server that had my MX record (which changed from Network Solutions to MS 365). Network solutions still has my “A record.”
2) Client says because my A record is still with Network Solutions, some servers on the internet are not yet propogated correctly to see that my MX record is hosted elsewhere.
3) Client’s primary DNS server is FirstComm (their ISP). MS 365 may want to check to make sure FirstComm servers update MS 365 records (MX and A records) correctly.
4) The problem was caused because my A records and MX records are SPLIT or because some servers (such as MS 2003 servers) do not update records dns records properly.
5) From the time the problem first started, email delays from client to me were 16 hours. This got reduced to 3 hours as servers “learned” my MX record had been changed but never got down to minutes as it should be until client moved the Microsoft exchange server got moved up in their list of exchange servers. There was no delay in client receiving emails from my MS 365 account to the client.
Hope this forensic analysis helps you to avoid this in the future.