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