Philip Miller <millenix(_at_)zemos(_dot_)net> wrote:
Send-only mail servers MUST also be registered in the
MX records,
and they should be given the lowest possible MX
priority (65535).
I don't think this is a new idea; I remember a similar
proposal by DJB some
time back, although I can't find it now.
I believe it's been discussed multiple times on this list, and
generally rejected, for the reasons you cited.
This was the basis of the original Paul Vixie proposal.
There are a number of problems,
1) There may be too many mail servers for the resulting mx records to fit
into a 500 byte UDP packet.
2) It requires active management of the mx list to include outgoing mail
servers.
3) Mail programs may attempt to deliver to the outgoing servers.
4) It is bad practice to redefine the semantics and functionality of
deployed infrastructure.
Phill
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