When sending mail you may get an error from the remote SMTP server saying something like 'Invalid HELO name'

This happens if the host name configured in VPOP3 does not look like a valid Internet host name (e.g. 'mail.domain.com'). Some SMTP servers don't bother checking this value because it has no authentication value at all, but a few do check that it looks correct.

To correct this, in the VPOP3 settings go to Settings → Misc Settings → General and correct the VPOP3 Host Name value. Normally you can just put a name which looks like a valid host name - e.g. mail.<your domain> (mail.company.com).

If you can, it can be better to use the actual Internet host name of your mail server and have a reverse DNS value set up pointing to your IP address with that same name in it, but this is usually only useful if you have VPOP3 sending outgoing mail using MX routing. It may not be possible in many cases (for instance, if you have a dynamic IP address or don't own your own domain)

It is not necessary for the VPOP3 host name to bear any relationship to the email addresses being sent out from that copy of VPOP3, but in many cases they will be in the same domain.