# Note: You must have PCRE support support built in to Postfix at
# compile time to use this.
#
# No, you won't find this entry in my "smtpd_recipient_restrictions,"
# above.  I'm not doing this check (at this time).

# If you want to be really picky about it: HELO'ing with an IP
# address is RFC-compliant - *if* it's enclosed in square-brackets
# ("[]"s).  (One would think "reject_invalid_hostname" checks for
# this, but it does not.)
#
# Somebody HELO'ing with a non-RFC-compliant dotted-quad IP
# address?  For shame!  (I don't do this check, btw.)
/^[0-9]+(\.[0-9]+){3}$/     REJECT Invalid hostname