There is a weird problem that I cannot think of any solution. There is a mail server Xs that has couple of domains on it and it is in Datacenter Xd. And there is a mail server Ys that has couple od domains also in another Datacenter Yd.
For only 1 domain and 1 user account the mail dont come. For instance;
tommy(at)domain(in)Xd.com
can send
alice(at)domain(in)Yd.com but cannot send hardy(at)domain(in)Yd.com
we tried numerous things and at last we deleted the accounts and created them again, but problem still exists.
What do you think has happened to these accounts ?
If you're running both sets of servers it might be an idea to start looking at your logs.
To catch all the likely obvious problems:
Hopefully somewhere in the above you should find a logged report that explains why the mail isn't getting through. Two other things to check: make sure the sending machine can resolve the receiving mail host's address (if this is the issue you should see the mail sat in the outgoing queue for a while with an appropriate error logged, and after said while you should get an error mail back from the sending server saying it has given in) and that the sender isn't on so many blacklists that the receiver just throws the incoming mail out without even dumping it in the junk folders.