I have a domain that is/was on Google's Workspace. The email MX records were pointing to their 5 servers. Now I'm trying to change the MX records that were pointing to the Google Workspace to my new VPS server. I deleted all of the MX records and added one MX record pointing to my new server. When I check 'host xxxx.com' and it does show the new server but when I check it again it's reverted back to the 5 google servers. And when I send mail to that account it still goes to the google email. When I do a dns check it shows that the new MX record has populated throughout the world. Very confused. I created another website in ISPConfig that is brand new and never touched google's email servers and it's working fine. mail gets delivered and sent fine.
When the e-mail sender checks MX record and receives the Google servers, the e-mail is sent there. If you have changed the MX to point to your new server, this change should be visible when you check what info is in name service. The reverting back part is strange, are you sure about it? Perhaps you change did not actually work?
I just needed to wait a couple hours. Even though with dnschecker.org it was showing that it was populated all over Google was hanging on to the old address. It went like this: I would check 'host xxx' and it would show the new MX destination then I sent an email to the address in question (that I had just changed the MX record for). That email would show up in the Google email account (and not on my new ISPConfig server) and right away I would check 'host xxx' and it would show the google email servers. I would wait a few seconds and check 'host xxx' again and it would show the correct new MX destination. Very weird but now everything is fine so I just needed to give it some time for Google to switch over.