On Fri, 4 Jan 2008, John C Klensin wrote:
There are no MX rules at all about which address must be tried first and
some handwaving in RFC 2821 about how many addresses at a given
preference level need to be tried at all.
In practice MTAs often randomise host addresses, ignoring the requirement
in RFC 2821 that they should trust the resolver to order them by
preference. You need to limit the number of host addresses your MTA tries
because some abusive DNS setups can cause an MTA to spend ages
wasting time trying to deliver a message. If you implement a limit like
this then it helps if you also randomize so that the next delivery attempt
tries a different subset of the host addresses.
Tony.
--
f.a.n.finch <dot(_at_)dotat(_dot_)at> http://dotat.at/
IRISH SEA SHANNON ROCKALL MALIN: MAINLY SOUTHWESTERLY, BECOMING CYCLONIC FOR A
TIME IN SHANNON, ROCKALL AND MALIN, 6 TO GALE 8, OCCASIONALLY SEVERE GALE 9,
PERHAPS STORM 10 LATER IN SHANNON, ROCKALL AND MALIN. ROUGH OR VERY ROUGH,
OCCASIONALLY HIGH. RAIN OR SQUALLY SHOWERS. MODERATE.
_______________________________________________
Ietf mailing list
Ietf(_at_)ietf(_dot_)org
https://www1.ietf.org/mailman/listinfo/ietf