So, what should I do when sending the HELO/EHLO command again?
If you want people to accept your mail, send the FQDN of the public
address from which the mail is emitted. In theory, the RFC says not
to reject on a bad HELO string, but in practice it's a rather strong
indication that mail is coming from a spambot or an abandoned and
easily abused old MTA.
Remember, it's not anyone else's problem if you've chosen to use
software that is hard for you to configure.
ietf-smtp mailing list