sendmail, 4th Edition

Rules Are Treated Like Addresses

After each side (LHS and RHS) is expanded, each is then normalized just as though it were an address. A check is made for any tabs that might have been introduced during expansion. If any are found, everything from the first tab to the end of the string is discarded.

Then, if the version of the configuration file you are running is less than 9 (that is, if the version of sendmail you are running is less than V8.10), RFC2822-style comments are removed. An RFC2822 comment is anything between and including an unquoted pair of parentheses:

[e-mail] (Operator)
R $A  tabRHS
   ↓
R [e-mail] (Operator)  tabRHS        ← expanded
   ↓
R [e-mail]  tabRHS        ← comment stripped prior to version 8 configs only

Finally, prior to V8.13 (see the next section, As of V8.13, rules no longer need to balance on page 653, for V8.13 and later behavior), a check was made for balanced quotation marks, and for right angle brackets balanced by left.^[247] If any righthand character appeared without a corresponding lefthand character, sendmail printed one of the following errors (where configfile is the name of the configuration file that was being read, number shows the line number in that file, and expression is the part of the rule that was unbalanced) and attempted to make corrections:

configfile : line number: expression  ...Unbalanced '"'
configfile : line number: expression ...Unbalanced ''

Note that prior to V8.13, an unbalanced quotation mark was corrected by appending a second ...