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
HELO250 oldsite.uofa.edu Hello here.ufa.edu [22.214.171.124], 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:
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). 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.
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)
bool is of type Boolean. If it is absent, the option defaults to true (do allow the hostname ...