Hi,

We have our exchange server's external DNS record updated by our DNS provider this morning. The TTL is 10 minutes. I can confirm the DNS record has been updated by checking it from http://www.mxtoolbox.com/

For example, the old DNS record is mail1.domainA.com A xxx.xxx.xxx.xxx

the new DNS record is mail2.domainB.com A xxx.xxx.xxx.xxx (same IP)

The DNS provider remove the old DNS record in domainA and add new DNS record in domainB.

However when I sent a test email using this exchange server and on receipts site it still say it is coming from mail1.domainA.com. I've checked this with our DNS provider, who suggested me to check with the exchange settings. 

Could anyone please advise what do I need to check within the exchange server? Or it is just simply the replication delay?

Thanks in adv

On Exchange server, from command line, flush the DNS

ipconfig / flushdns

In Active Directory DNS, right click on the top-most DNS node of your domain and choose "Clear Cache." Those two settings should clear every old remnant.

Aside from that, as you mentioned, there may be some delay, but I think clearing DNS cache and flushing DNS should do the trick.

Worst case, you may also need to Reboot your Exchange server.

OOPS! I forgot: ALSO CHECK YOUR "MX" (Mail Exchange) record!

It will be in your DNS and in the DNS of your provider - so, make sure you update your MX record and that your ISP updates the record on their end - that's likely the issue.

I hope I was helpful. Please Mark as Answer if I helped resolve your issue.