sendmail, 4th Edition

AllowBogusHELO

Allow HELO or EHLO sans host V8.8 and later

Prior to V8.7, sendmail would accept without complaint an SMTP HELO command (or an EHLO) that omitted the hostname:

220-oldsite.uofa.edu  Sendmail 8.6.13/8.6.13 ready at Fri, 13 Dec 2002 08:11:44 −0700
220 ESMTP spoken here
HELO
250 oldsite.uofa.edu Hello here.ufa.edu [123.45.67.89], pleased to meet you

RFC1123, Section 5.2.5 specifies that all HELO and EHLO commands must be followed by a fully qualified hostname:

HELO here.uofa.edu
EHLO here.uofa.edu

Beginning with V8.7, omitting the hostname results in one of the following errors:^[365]

501 5.0.0 HELO requires domain address
501 5.0.0 EHLO requires domain address

Note that there is no check to see that the hostname is actually that of the connecting host unless PICKY_HELO_CHECK is declared when sendmail is compiled (PICKY_HELO_CHECK on page 133). Also note that the specified hostname must appear to be a correctly formed hostname. If it is not, the following is printed:

501 5.0.0 Invalid domain name

If you favor forcing other sites to obey the RFCs, don’t enable this option. But note that you might need to enable it if your site accepts connections from other sites that don’t obey the protocols.

The AllowBogusHELO option is used like this:

O AllowBogusHELO=bool                         ← configuration file (V8.8 and
later)
-OAllowBogusHELO=bool                         ← command line (V8.8 and later)
define(`confALLOW_BOGUS_HELO', `bool')        ← mc configuration (V8.8 and later)

The bool is of type Boolean. If it is absent, the option defaults ...