Sendmail's basic interface is straightforward. It takes a ton of flags, but most are rarely used. qmail's sendmail emulation only supports these flags:

• -fsender sets the envelope sender, and the header From if it's otherwise unset.
• -Fsender-name sets the name in the header From, if it's otherwise unset
• -t says to get the envelope sender and recipients by parsing the message headers.
• -bp says to print the queue
• -bs says to provide SMTP on stdin/stdout
• other flags are ignored
• other non-flag arguments are envelope recipients.

Message is read from standard input. That's about it.

Update: Fixed formatting.