CHAPTER 26 Mail
Within sendmail.cf one macro might specify your Internet subdomain, e.g.:
## Change the D and E macros to accommodate your subdomains.
## Note that this configuration will do its very best to generate all addresses as coming from $D.
The "D" in the first column "defines" the following D and E as acs.ohio-state.edu and ohio-state.edu, respectively. These can be recalled later in the file as $D and $E.
Another macro might specify the style of a header line, e.g.:
## Pick one of the next 2 lines, based on your syntactic preference for
## "firstname.lastname@example.org (Joe Random)" or "Joe Random <email@example.com>".
And still another might specify where to forward BITNET mail:
# Strange nonstandard nets - attempt to hand to forwarder.
The syntax of the re-writing rules is explained in the Sun AnswerBook Mail Administration Guide and in the book sendmail by Costales, et.al.