I have recently setup a new Exchange 2013 server to take the place of an older 2013 server. I have migrated the mailboxes over, changed the DNS to point to the new server (both internal and external), have uninstalled Exchange from the old server and, all is working.

That is until I shut down the old server, and mail stops flowing into the new email server from our antispam gateways.

I can only asumme that the Exchange config has a reference to the old server but I can't find where. I have checked all the visible setting on the send and receive connectors but can't find anything.

Any idea on where I should

Hi Simon,

Possible checklist to identify the Issue

1) Enable logging on your SMTP Filtering Gateways and see to which IP's, HostNames they are delivering the emails. Make sure that they are delivering to new  Exchange 2013 servers.

2) Do a message tracking for any external emails  on the new Exchange 2013 servers and see whether you are getting any results. This will tell you whether Exchange is receiving external emails.

3) Enable protocol logging on receive connectors on exchange 2013 servers and see if you are getting any informations.

4) Telnet from your SMTP gateway to your Exchange 2013 servers and see if you are getting any responses. 

I ran some of these checks and everything seemed fine. After logging in to my gateway antispam servers and running a dig command to check the DNS resolution to my new exchange server it started working. May have been cached DNS records.

Which is strange because the DNS was updated about 36 hours ago, and doesn't explain why it worked when the old server was running as it no longer has Exchange running on it.

I think I'll chalk it up to the joys of working with computers :)

Thanks for the tips Satish