This article explains how you can fix the error 'This address no longer accepts mail on your 123 Reg Server'.
Please note: this article was originally created for our previous generation of Virtual Private Servers. As such, these instructions may not be relevant to our current generation of Virtual Private Servers.
Plesk/Qmail
Generally this error happens when mail for the domain was hosted on the server at some point, but has since been moved to an external mail server. Qmail will still try to deliver the message locally and fail with this error:
This_address_no_longer_accepts_mail
The Fix
To correct this check the following two files for the domain in question:
/var/qmail/control/rcpthosts
/var/qmail/control/virtualdomains
Remove any lines with the domain which is causing the error from both files and then restart Qmail:
/etc/init.d/qmail restart