A server I'm taking care of uses qmail for MTA. I can send and receive to almost every domain except one or two that give the following error, or something very similar:
550-Verification failed for <email@example.com> 550-No Such User Here 550 Sender verify failed
From what I understand from this article the remote host tries to send an email to my host to see if the mailbox really exists.
I tried the same commands with telnet from my laptop, and i get
250 ok answers, leading to think that the user does indeed exist.
Why then does the remote host not get the same response I did?
How can I check if traffic from the remote host is indeed routable to my sending host?
Any other sugggestions?