On Fri, Apr 04, 2008 at 11:21:46AM -0700, Paul Hoffman wrote:
Or, you can be more specific. What is the problem of a host that is
never expected to be on the RHS of an email address expected to have
an MX record? That's an honest question, given that it has been over
12 years with the current setup.
This message came from owner-ietf-smtp(_at_)mail(_dot_)imc(_dot_)org, which is
We need to find the place to drop a return-to-sender:
Before 2821: lookup an MX record for $RHS
If not found: lookup the address of $RHS and pretend it was an MX.
During 2821: lookup an MX record for $RHS
If not found: lookup the A-record(s) for $RHS and pretend it was an MX.
After 2821: lookup an MX record for $RHS
If not found: currently under debate.
a) stay with looking up A-records (i.e. no AAAA fall back, only A)
b) change back to looking up addresses (i.e. A and AAAA fall back)