Computing 'Date:' header only when sending

Hi all,

Consider the following scenario: I regularly send (almost)
exactly the same message once a week. So I select the last message I
sent, hit Ctrl-E to edit it, apply slight changes if needed, and hit the
'Send' button.

My expectation is that the 'Date:' header will reflect the time at which
I send the *new* message, not the time at which I sent the old one.

Moreover, section 3.6.1. of RFC 2822 states:

   The origination date specifies the date and time at which the
   creator of the message indicated that the message was complete
   and ready to enter the mail delivery system.  For instance, this
   might be the time that a user pushes the "send" or "submit"
   button in an application program.

Those two reasons lead me to change the way my local copy of M
generates 'Date:' headers. It's generated in only two siturations:
the message is a 'resent' and has no 'Date:' header already (this
should actually not happen, as 'Date:' header is mandatory), the
message is not a 'resent' and will actually be sent right now
(rather than put into Outbox).

The most visible changes are:
- Draft messages do not have a 'Date:' header any more.
- A user-specified 'Date:' header will be ignored and overwritten. 

Should I commit this change?