You get that error when the forums can't see the mailserver.
UPDATE:
I've gotten the IP changes done, and everything looks as it should. We should be 100% in about 24 hours, but as of now everything on our side is up and running.
Mail should be either working, or it will be working pretty soon, as it's 12:34am here and I'm still up tweaking, making sure everything is , indeed, working.
So, once I've confirmed mail flow, we should be good to go.
Regards,