reject_invalid_helo_hostname
Would reject an invalid host name such as "ho+st", but a valid hostname such as "host" would pass (https://datatracker.ietf.org/doc/html/rfc2821#section-2.3.5):
501 5.5.2 <ho+st>: Helo command rejected: Invalid name
reject_non_fqdn_helo_hostname
Would reject a non fully-qualified hostname such as "host", but a fully-qualified one such as "host.domain.tld" would pass:
504 5.5.2 <host>: Helo command rejected: need fully-qualified hostname Cheers, K.
