I've been tearing my hair out over this for the past day or so.
I've setup a zimbra box (mail.ukwebsystems.co.uk) and setup an A record in the DNS to point to the right IP. I've setup the MX records to point to mail.ukwebsystems.co.uk.
I've got the ISP to setup a reverse DNS entry for the IP of the server (delenn.ukwebsystems.co.uk).
But when I try and send anything from my current mail server (i.e. to the Zimbra box), it just comes back as an unrouteable address. I've tried it from my ISP's smtp server and it says the same.
I logged into my current mail server and can ping the Zimbra box, I can telnet into it on port 25 - basically, the current mail server can talk to the Zimbra box.
When I try and send mail from the Zimbra box to the current mail server, the current mail server rejects it...
help!This is the mail system at host mail.ukwebsystems.co.uk.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can
delete your own text from the attached returned message.
The mail system
/email addr removed/: host ukwebs64.positive-dedicated.net[18.104.22.168]
said: 550-Verification failed for <firstname.lastname@example.org>
550-Unrouteable address 550 Sender verify failed (in reply to RCPT TO