The reply command is a slightly easier way to send a reply than using the send command. After reading the message, type reply or just r at the R> prompt:
Message 73 (378 chars) Return-Path: <jb51> Received: by cunixf.cc.columbia.edu (5.59/FCB) id AA01344; Monday, 7 Sep 92 10:50:29 EDT Date: Monday, 7 Sep 92 10:50:28 EDT From: Joe Brennan <email@example.com> To: fb2 Cc: mm33, hk12 Subject: Meeting on Sept 21 Message-Id: <CMM.firstname.lastname@example.org> Let's meet on Sept 21 at 2:00 to go over plans for this semester. Joe R>reply Message (End with CTRL/D or ESC Use CTRL/B to insert a file, CTRL/E to enter editor, CTRL/F to run text through a filter, CTRL/K to redisplay message, CTRL/L to clear screen and redisplay, CTRL/N to abort, CTRL/P to run a program and insert output.): OK, I can meet then. --Fuat [escape] [ D=display S=send TE=text ED=edit TY=type Q=quit ?=Hints HELP ] S>send jb51... Queued R>
As you can see, reply is similar to send, but you skip over the prompts for To, cc and Subject. The reply goes to the address in the From field of the message you received, and it has the same Subject field.
At the S> prompt, you can type quit if you decide not to send the reply after all.