Strict Syntax Parameters
There are two parameters configured in main.cf that require strict adherence to Internet email
standards. Enable the smtpd_helo_required parameter to require that SMTP clients start the conversation with the HELO/EHLO verb, as described in the SMTP RFC. By
default Postfix is rather lenient with clients that do not follow the
protocol exactly. If you specify smtpd_helo_required = yes, and a client skips
this step, Postfix rejects the message. The RFC also specifies exactly
how envelope addresses should be formatted. Normally, Postfix
accepts nearly any envelope address that it can make sense of, but if
you specify strict_rfc821_envelopes =
yes , Postfix rejects messages from clients that do not send
correctly formatted addresses.
In actual practice, it’s probably a good idea to require HELO because most clients at least follow the
basic steps of the protocol. On the other hand, there are a number of
clients that don’t get address formatting correct. Being too strict here
might lose legitimate messages.
Get Postfix: The Definitive Guide now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
