Extensions to SMTP

Carlos Antunes | 1 Mar 1995 12:03

Re: Internet draft draft-onions-822-mailproblems-00.txt


In article <EjIs7AO00WBwMZynIj <at> andrew.cmu.edu>
jgm+ <at> CMU.EDU (John Gardiner Myers) wrote:
> 
> code.  It also does MX randomization and MX piggybacking.  It does do
>                     ^^^^^^^^^^^^^^^^     ^^^^^^^^^^^^^^^

Can you please explain this strategies?

Thank you!

Regards,
Carlos Antunes.

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Craig_Everhart | 1 Mar 1995 17:26

Re: Internet draft draft-onions-822-mailproblems-00.txt

Excerpts from transarc.system.ietf-smtp: 1-Mar-95 Re: Internet draft
draft-on.. Carlos Antunes <at> individua (743*)

> > code.  It also does MX randomization and MX piggybacking.  It does do
> >                     ^^^^^^^^^^^^^^^^     ^^^^^^^^^^^^^^^

> Can you please explain this strategies?

MX randomization:

Suppose a destination mail domain A has multiple MX destination hosts
(X, Y, Z) with equivalent preference values.  These hosts should be
tried in a random order when trying to deliver mail to domain A, not
simply the order in which they appear in the DNS response.  This applies
even if there are other destination hosts for A with other preference
values; when trying the hosts of a given preference value, they should
be tried in random order.

MX piggybacking:

Suppose that multiple mail domains (A, B, C) have overlap in their MX
list of destination hosts.  In general, mail may be delivered for more
than one mail domain while connected to a single destination host.  If
it's the same piece of mail that's being delivered, these multiple mail
domains may be given as multiple RCPT TO commands for the same MAIL
FROM/RCPT TO/DATA transmission.

Of course, all the MX priority rules for each mail domain must be
followed, but you can still achieve substantial overlap.  When I did an
early version of this code, it was motivated by a lot of mail domain

(Continue reading)

headers

John Gardiner Myers | 1 Mar 1995 17:56

MX strategies

MX randomization: between different attempts to process a queue entry,
same-valued MX records are ordered randomly.  This distributes load
evenly across different same-valued MX records

MX piggybacking: when two or more domains have the same ordered set of
MX records, those domains are considered the same for purposes of
combining multiple RCPT commands in one transaction.

(A more clever SMTP client which caches delivery failures could do a
more effective piggybacking optimization than that described above.)

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