The sendmail program implements the SMTP (and ESMTP) HELP command by looking up help messages in a text file. Beginning with V8.7 sendmail, help messages for the -bt rule-testing mode are also looked up in that file. The location and name of that text file are specified by using the HelpFile option. If the name is the C-language value NULL, or if sendmail cannot open that file for reading, sendmail issues the following message and continues:^[33]

^[33] That is, if it is in a safe directory, and if the file itself is safe. See the discussions under the DontBlameSendmail option, specifically See this section.

502 5.0.0 HELP not implemented

The help file is composed of lines of text, separated by tab characters into two fields per line. The leftmost field is an item for which help is offered. The rightmost field (the rest of the line) is the help text to be printed. A few lines in a typical help file might look like this:

help    HELP [ <topic> ]
help            The HELP command gives help info.
helo    HELO <hostname>
helo            Introduce yourself.
ehlo    EHLO <hostname>
ehlo            Introduce yourself, and request extended SMTP mode.
ehlo    Possible replies include:
ehlo            SEND            Send as mail                    [RFC821]

For an SMTP request of help vrfy, sendmail might produce:

214-VRFY <recipient>
214-     Verify an address.  If you want to see what it aliases
214-     to, use EXPN instead.
214 End of HELP info

The forms of the HelpFile option are as follows:

O HelpFile=file           configuration file (V8.7 and later) 
-OHelpFile=file           command line (V8.7 and later) 
define(`HELP_FILE',`file')    mc configuration (V8.7 and later) 
OHfile                    configuration file (deprecated) 
-oHfile                   command line (deprecated) 

The argument file is of type string and can be a full or relative pathname. Relative names are always relative to the queue directory. If file is omitted, the name of the help file defaults to helpfile. If the entire option is omitted, the name of the help file is undefined. The default for the mc configuration technique is /etc/mail/helpfile. SMTP is described in RFC2821, and ESMTP is described in RFC1869.

The HelpFile option is not safe. If specified from the command line, it can cause sendmail to relinquish its special privileges.