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On 8 May 2008 at 18:50, Tony Finch <dot(_at_)dotat(_dot_)at> said:
On Thu, 8 May 2008, Robert A. Rosenberg wrote:
OTOH, if/when the highest priority is ONLY CNAMEs (even if lower/back-up
MXs are A/AAAA which you can support) do an immediate reject since the
back-up MXs will never be able to deliver to the primary servers (due to
their being invalidly defined as CNAMEs).
That's not necessarily true: (1) Backup MXs don't have to use the standard
routing algorithm to deliver email. (2) If the verifying MTA is IPv4-only,
the primary MX is IPv6-only, and the backup MX is dual-protocol, your
proposed algorithm will falsely bounce the message.
The backup MXs you didn't plan on sending mail to may, furthermore, not
mind CNAMEs, even if you do. From the implementation point of view,
CNAMEs can be highly transparent.
To make this algorithm work, you have to intentionally look for an error
condition at the primary. You would no longer be seeking a next hop
within your IPvX capabilities only using the standardised search. I think
that's outside my scope for a clean implementation, but others may feel
differently.
Cheers,
Sabahattin
- --
Sabahattin Gucukoglu <mail<at>sabahattin<dash>gucukoglu<dot>com>
Address harvesters, snag this: feedme(_at_)yamta(_dot_)org
Phone: +44 20 88008915
Mobile: +44 7986 053399
http://sabahattin-gucukoglu.com/
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