> These commands are used to identify the SMTP client to the SMTP > server. The argument field contains the fully-qualified domain >name of the SMTP client if one is available.
when is a fqdn not available? That's not even the more troublesome reverse domain, it's the in forward domain. >In situations in which the > SMTP client system does not have a meaningful domain name (e.g., >when its address is dynamically allocated ... which means it can't be mail server for inbound MX traffic. >4.1.3 Address Literals > > Sometimes a host is not known to the domain name system .. and therefore it's not a mail server we want to accept mail from. This whole "ip as helo command hostname" sideshow is bogus excuse-making. It is not "best practices" and the above "exceptional" cases qualifies the SMTP client sending IP as helo as rejectable, in the current, forever worsening Internet mail environment. Again the best practices/credentials are for a machine emitting email are: IP has a PTR hostname, which has .... A record matching the IP ... and the SMTP client says helo with the PTR hostname. None of the above has anything to do with @sender.domains emitted by the SMTP client, nor with any MX records. Len
