First off, thank you in advance for reading this essay and offering any help you can provide. I am 100% stumped and my client is really, really frustrated.
I have a client who was using an offsite Exchange server. The IT provider who hosted it had an Exchange 2003 server set up, along with a terminal server in Texas that my client would RDP into. The service did not work reliably and my client was unhappy and unable to do any work for 90% of the day.
Two years ago they asked me to deploy an onsite Exchange 2013 server for them and migrate their Exchange data from the old server to the new server. The old email/rdp provider would not give me admin access and tried to charge my client $25k for 'offboarding'
so instead of paying them, we opted to create PST files for each user from the old server, copy them to a local computer and use the PST capture tool to import them into a new set of mailboxes on a new domain.
Initially we had an issue where internally if anyone replied to an old email it would use an old x.400 entry (pulled from the NK2 files we brought over, I assume) and create a new nk2 entry (or whatever they are called now) for that user which would in turn make all email going to that autocomplete entry fail because it was looking for the old Exchange server. We had to make them all type in the (again, internal only) addresses on any replies for a few months to prevent them from making any new NK2 entries based on those old addresses and we manually delete all of the old nk2 entries.
Regarding external to internal email, we've never had a single issue with email being routed to the new server correctly.
I give all of that information as context. We now have a VERY bizarre issue that I haven't seen before and I am not sure if it is related.
A few weeks ago, some users started claiming that they weren't getting responses from some clients who are sending external to internal (internal to internal users aren't a problem.) These are clients which they have never had a problem getting email from
before. A bunch of their clients can't email them at all. Outgoing emails from our Exchange 2013 server to these clients go through. Incoming emails from most external addresses come through (I can email them fine) but for the companies who are affected, the
email doesn't hit our server at all.
I've been able to get some of the NDRs from some of these clients. One in particular today has me thrown for a loop. It is an NDR from my client's old Exchange/RDP provider. It says:
Generating server: TX2CH009.myxt.net
christine@XXXXXXXXXX.com
#550 5.1.1 RESOLVER.ADR.RecipNotFound; not found ##
john@XXXXXXXXXX.com
#550 5.1.1 RESOLVER.ADR.RecipNotFound; not found ##
That myxt.net is their old provider and that hasn't been used for over two years.
What I can't figure out is how or why email is being routed to the old server. Our DNS is hosted at networksolutions and all of the records are correct. Doing an MX lookup shows the correct records. Using the Microsoft RCA shows that everything works fine. My guess is that one of two things is happening:
1) Networksolutions is messing up DNS and routing some email to the old server even though that DNS record hasn't existed in two years
2) There is some part of Exchange that I somehow have misconfigured to blast email out and show the old server as the place to route email (which doesn't make sense but what do I know) and therefore email being replied to get routed to the old server somehow
3) Somehow the old server's mx record is cached on these clients internal dns servers (which again doesn't make sense to me as it all worked up until three weeks ago and nothing has changed.)
Thanks for reading this horribly long post. If anyone has any ideas I am 100% stumped and feeling 100% stupid by this. My client is 100% pissed and that's a total of 300% misery for everyone involved.