Update man page

man/fmail.1.in

@@ -29,7 +29,25 @@ fmail \- mail formatter
 .PP
 .B fmail
 formats text read on standard input into a mail message
-ready to be sent to a mail sending agent.
+ready to be sent to a mail submission agent.
+.PP
+The formatting process includes: encoding the text body in
+.I Quoted-Printable\fR;
+creating appropriate MIME parts for attachments and
+OpenPGP signature; encoding attachments (in
+.I Base64
+or
+.I Quoted-Printable
+depending on their type); adding appropriate mail headers.
+.PP
+The resulting message is printed on standard output and can
+be piped directly to a program such as
+.B sendmail(8)
+to effectively send the message to a mail server.
+.PP
+The first lines of the input message, up to the first blank
+line, are treated as mail headers; everything from the first
+blank line to the end of file is treated as the mail body.
 
 .SH OPTIONS
 .TP