command-line switch causes sendmail to gather
its list of recipients from the message's header in
addition to gathering them from its command line. The
-t switch takes no arguments.
When this switch is specified, sendmail gathers
recipient names from the To:,
Cc:, and Bcc: header lines. It
also gathers recipient names from its command line if any were
listed. Duplicates are discarded, the Bcc: header
is stripped, and the message is delivered.
The -t switch is intended for use by MUAs. It
should never be specified when
sendmail is run in daemon mode.