Sometimes it's important to make email look like it came from another site. Sendmail has some limited but important capabilities to make this happen.
Email contains header lines reflecting the host where the mail originated.
Masquerading email rewrites email headers to look like they came from somewhere else. Masquerading email can cause a good deal of mischief if performed improperly. This guide will show simple ways of avoiding that mischief. Masquerading can be used to simplify email routing by forcing all email to look like it came from a central hub. This also simplifies management of email systems because then a small number of machines need email servers instead of every machine.