When sendmail logs
the recipient's record, it will include the identity
of the controlling user, if there is one. A controlling user is set
when delivering to files or through programs (Section 12.2.2):
ctladdr=<you@your.domain> (111/22),
The controlling user is printed as an address, the
<you@your.domain >, although it could also
be a local login name when mail originates locally (such as
you). If the controlling user is the identity of a
local user, the uid (the 111) and the
gid (the 22) for that user are also logged.
