On Thu, 8 May 2008, Robert A. Rosenberg wrote: > > If there are two or more MX records at the highest priority (ie: preferred) > and some point at CNAMEs and some point at A/AAAA then while the MXs are > partly broken, the CNAMEs can be ignored (ie: Treated as Unreachable) and the > A/AAAA records used for those addresses you have IPvX connectivity for. If > none are usable then reject.
Yes, that's what RFC 2821 says. > 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. Tony. -- f.anthony.n.finch <[EMAIL PROTECTED]> http://dotat.at/ SHANNON: SOUTHWEST 3 OR 4 BECOMING VARIABLE 3 OR LESS. MODERATE. SHOWERS, FOG PATCHES. MODERATE OR GOOD, OCCASIONALLY VERY POOR.
