PICKY_HELO_CHECK

PICKY_HELO_CHECK

---

Make sendmail picky about HELO

tune with confENVDEF

The SMTP HELO command is used to introduce the calling machine to the receiving machine. The form of that command is:

 HELO  calling host name here  

Note that HELO and EHLO are equivalent in this regard. Ordinarily, sendmail doesn't care what the calling host calls itself. All sendmail cares about is that this name is the canonical name of a machine. If you care whether the HELO hostname matches the real hostname of the calling machine, you can add a line such as the following to your Build m4 file:

 APPENDDEF(`confENVDEF', `-DPICKY_HELO_CHECK') 

With PICKY_HELO_CHECK defined, a mismatch (other than the local machine calling itself localhost ) will cause the following warning to be logged:

 Host  realname  claimed to be  heloname  

Note that this check is ordinarily turned off because a large number of hosts on the Internet use a name that is different from their canonical name. ^[7]

^[7] Eric was getting complaints that the continual insertion of this warning was misleading and tended to cause people to ignore it entirely.