Re: Default for the envelope From in smtpmail.el

[Stephen J. Turnbull]

Glenn Morris writes:

 > Now you send it. The envelope from address (which is used eg for the
 > MAIL FROM command sent to the stmp server) should default to whatever
 > was in the From: header.

This is a bad idea.  Emacs should set the envelope address only on
specific request from the user.  Provide an easily customized option,
yes.  Default, no.  The default is to let the MTA figure it out.

Users who change the From address had better know what they are doing.

 > At the moment, it effectively defaults to user-mail-address.

Don't you have this backward?  The envelope address is set by the MTA,
which defaults to using the mailbox of the logged-in user.  This
corresponds to user-mail-address because user-mail-address defaults to
the same value.  (I don't know or care what smtpmail.el currently
does, but here it is functioning as an MTA.)

Note that on some systems unprivileged users using the system MTA may
not be able to set the envelope address at all.

 > > If the proposal is for not using it only in smtpmail.el, then we need
 > > to verify that there are no valid use cases without a 'From:' header
 > > in the current buffer.

A mail message must have a From field to conform to RFC 5322 (see
table on p. 20 of that RFC).

Steve