Address to DNS mapping

Gentlemen,

I'd like to raise another question, which everybody silently
passed in the drafts (including myself in my earlier drafts).

Ignore for a moment, what and how we do the lookup. I'd like
to focus on _where_ we do the lookup.


When we receive a MAIL FROM: (or HELO) command, it's argument
is some random text string. Whether we do RMX, DRIP, SPF, all need to 
do a DNS lookup, and we all assumed to just cut the domain part from 
the address and use it as the place where to look at in the DNS.

I don't think anymore that it is quite that easy:

- We need to cope with empty sender addresses (coming with
  error messages),

- sender addresses without domain 

- empty domain

- malformed addresses (we need a syntax)

- Should we cut off the name part? Why not allow lookup of the
  full address? And if so, how to avoid ambigousity?

- What about encoding?


regards
Hadmut