Imagine that RFROM wasn't a parameter to MAIL, but that it was a command
in and of itself, given after MAIL and before RCPT: Then you could have
multiple RFROM's for any message.
Whoa, I'm glad you brought this up... I just realized that making RFROM a
seperate command (between MAIL FROM and RCPT TO) would make MTA integration a
lot easier on some platforms.
For example, hooking the "MAIL FROM" command allows you to get the RFROM
parameter, but the command may still need to continue on to the next layer or
the MTA itself (for address verification or envelope creation). Unfortunately,
the next layer or MTA doesn't understand the RFROM parameter, so it ignores the
whole command or returns a "555 Unsupported option", which ruins everything.
If a seperate RFROM command can be used, then the SPF layer can handle it
without the command needing to be passed on to the other layers (which would
respond with an error).
Just something to think about,
Michael R. Brumm