We have been having problems sending emails from our mail server (running Kerio) to a particular domain over the past few weeks. We kept receiving bounce emails with the following:
550 Rule imposed. Sender using invalid hostname in greeting as per RFC specification.
After trying all manner of solutions, it turned out to be a problem with our Kerio setup. Lots of mail servers are being configured to only accept connections from Fully Qualified Domain Names (FQDN) – we had our mail server setup without a fully qualified address. So we needed to make the following change:
example.com => mail.example.com
To apply this change to our Kerio mail server, we simply changed the setting in Kerio using the following steps:
If you are using a different mail server, consult the associated documentation and ensure you have the mail server setup with a FQDN.