Prioritizing among MX records

[phn at icke-reklam.ipsec.nu]

Jan Koz?nek <jkozanek at totalservice.cz> wrote:
> Hello,

> I'd like to ask if anyone knows whether numbers in MX records are just=20
> positional values or real priority numbers.

> Let's say we have an example like this:

> bogus.com.    IN    MX    10    primary.bogus.com.
> bogus.com.    IN    MX    60    backup.bogus.com.
> bogus.com.    IN    MX    65    last-hope.bogus.com.

> Does it mean anything else than that under any circumstances, if mail=20
> relay will fail with primary.bogus.com, relaying will be tried to=20
> backup.bogus.com IMMEDIATELY and if that fails, it will be IMMEDIATELY=20
> tried to last-hope.bogus.com?

Under normal circumstances *some* mail will be delivered=20
to "higer-MX" due to various sources ( network disturbances etc),
the amount seems to depend on the "diversity" of the mailhosts.

I have observed in one organisation that has MX both in Europe
and US that US senders seems to prefer the US mailhost in spite
of "higer-mx".

> Is number of delivery retries to each of the mail servers dependent=20
> solely on the sending SMTP server's software?

> Reason for my question is that some time ago I found a material quoting=
=20
> that the priority number in a way affects also the number of failed=20
> retries a relaying SMTP will try with each mailserver, before falling=20
> back to the one with lower (higher number) priority. And, to my=20
> surprise, while testing, I discovered corelating speed-ups/speed-downs,=
=20
> which could justify the above statement.

There is no such "speedup" in rfc2821 ( afik) . What implementation
does this ?


> Thanks for clarification,
> Regards

> --=20
> S pozdravem/Best Regards,
> Jan Kozanek




--=20
Peter H=E5kanson        =20
        IPSec  Sverige      ( At Gothenburg Riverside )
           Sorry about my e-mail address, but i'm trying to keep spam out=
,
	   remove "icke-reklam" if you feel for mailing me. Thanx.