Pre-V8 versions of sendmail possessed many assumptions and restrictions that modern versions have fixed, added, or eliminated. Prior to Solaris 2.5, Sun used a sendmail that was based on V5 sendmail and highly modified to satisfy Sun's other enhancements to UNIX.
To support old configuration files that were based on that old version of sendmail, Sun offers the V1/Sun version configuration command. The backward compatibility that V1/Sun mode supplies is shown in Table 38.5.
When making DNS lookups, RES_DNSRCH (search subdomains) and RES_DEFNAMES (append the local domain) are automatically disabled.
Duplicate left-hand side entries in the aliases(5) file are silently ignored.
The VRFY and EXPN SMTP commands (see Section 22.3.2, "SMTP vrfy and expn") provide the same information. That is, they both act like EXPN.
A user with any shell is allowed to redirect mail to programs or files (see Section 22.8.4, "The /etc/shells file" for how this differs from current behavior).
Note that V1/Sun should be added to your old configuration file
only after you have upgraded to Solaris 2.4 or higher's version
of sendmail. The
V configuration command
will not be recognized by earlier versions of sendmail,
and that command can cause those earlier versions to fail.