We are in the process of migrating 15 domains underneath 1 master tenant. The first few went fine but we ran into an issue where the A record was not created and email would not go through. I know the first thing you will think of are all the basics (blacklist, proper DNS records, misspellings, typos, etc) but understand that if it were that simple we wouldn't be posting. We even registered with MXToolbox to walk through all the steps and possibilities and it all pointed to one thing. In the below picture where we now have an IP address with an associated A Record it at first said "No Record Found" under the IP Address column. Didn't matter what we did on our end this ip address would not appear.
The next thing people say is, well that's not a Microsoft address and Microsoft doesn't create those even though a DNS lookup says otherwise. So imagine our confusion when Microsoft said it's DNS on the client side and not a Microsoft issue. 8 days later with still no email we finally deleted the account and reregistered under a personal tenant. Immediately we got an A record, reverse PTR and IP address and email. Deleted and put back on the original tenant and now we have the ip that you see above and without us changing any configurations on the client side or with the hosting provider; just waited for it to finish replicating in the Admin portal after moving and it worked.
We get that you have to work through the steps to get to the problem but it seems as if we couldn't get anyone to take the steps to the next level when the steps aren't working. Our focus now is that we need a root cause and for someone to at least understand that this is so not a typical scenario. We need this escalated to an Engineer to help us figure out root cause or to provide a way to escalate (we are a Gold Partner and willing to pay) without being told to be patient while the client can't access email for over a week. The client is losing trust in Microsoft and it's hard for us to defend at this point. We have 10 more migrations and are nervous that we will be stuck in the same situation.