One
form of attack against sendmail involves
appending information to an existing qf file. To
prevent such attacks, V8.7 introduced the dot line. In a
qf file, any line that begins with a single dot:
.followed by anything
is considered to mark the end of the file's useful
information. Upon encountering that dot,
sendmail continues to read the
qf file. If any line follows the dot line,
sendmail logs the following message and changes
the qf file into a Qf file
(Section 11.5.3):
SECURITY ALERT: extra data in qf: bogus line here
