[EMAIL PROTECTED] wrote: > Basically, the premise is set an MX with a high preference pointing to a > system that does not listen on port 25. Broken mailers would attempt to > connect to it, fail, and not try a lower preference mail exchanger. A > real mailer would fall back to a lower pref MX.
[And add a low-preference non-functional MX too, to stymie spammers] [...] > What does the collective wisdom of the list think about Nolisting, and the > idea of a low preference MX record as well? In practice, it will probably be moderately effective. However, I would hesitate to have a non-functional host as my most-preferred MX machine. The relevant RFC (2821) is a bit waffly: When the lookup succeeds, the mapping can result in a list of alternative delivery addresses rather than a single address, because of multiple MX records, multihoming, or both. To provide reliable mail transmission, the SMTP client MUST be able to try (and retry) each of the relevant addresses in this list in order, until a delivery attempt succeeds. However, there MAY also be a configurable limit on the number of alternate addresses that can be tried. In any case, the SMTP client SHOULD try at least two addresses. It's not clear to me that an SMTP client that only ever tries the most-preferred MX host is in violation of the RFC. (It's violating a SHOULD, but is it violating a MUST?) Greylisting should be about as effective, but it won't prevent mail from a client that only ever tries the best MX host. Regards, David. _______________________________________________ NOTE: If there is a disclaimer or other legal boilerplate in the above message, it is NULL AND VOID. You may ignore it. Visit http://www.mimedefang.org and http://www.roaringpenguin.com MIMEDefang mailing list [email protected] http://lists.roaringpenguin.com/mailman/listinfo/mimedefang
