On Sat, 20 Sep 2003, Doug Royer wrote:
RFC 2821 (proposed standard) sheds some light on that: (This isn't a
replacement to STD0010, but reveals the disagreement on the roles of MTAs
and MUAs)
Your quote talks about conventions that may be used. It does not support
your view that the MUA and MTA have to be separate pieces of code.
If they aren't separate peices of code, how is it that their functions
will be separated? But assuming an MTA is bundled together with an MUA,
the MUA function must hand the message to the MTA function for routing.
The function of an MTA is still to return a bounce. The MUA functions may
not attempt to perform routing. So they cannot determine immediately if
the "domain exists".
And what your ISP does for your does not have to be what other ISPs do
for their customers.
I agree.
--Dean