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Re: [ietf-smtp] Address literals

2016-08-01 08:35:42
Alessandro Vesely <vesely(_at_)tana(_dot_)it> wrote:

1. If the host can resolve the address and obtain a domain name, it can
replace it so as to obtain a regular mailbox.  Right?

I think an MTA should not use the DNS at all to handle an address

2. If the host cannot resolve the address, it can either try to relay it or
try to deliver it locally.  What is the recommended behavior?

The literal either refers to one of the MTA's interface addresses, in
which case it should apply its own local rules (which might include
rejecting), or it refers to another host, in which case the MTA should
relay the message to the specified address if that is allowed.

I recommend that relaying attempts using address literals should always be
rejected, and local address literals should only allow postmaster as the
local part, and the MTA should treat it the same as bare <Postmaster>.

3. If in case (2) the server relays, it can either drop or keep the domain
part when it issues RCPT TO to its peer.  Dropping is conservative, as the
address literal has already be used, so it won't be used again in case the
peer is the server itself connected through a NAT or transparent proxy.

(a) don't relay :-)

(b) you should never rewrite addresses that don't belong to you

(c) if you want to make this work with NAT too then, um, why are you
    trying so hard to make something work that no-one will ever use? :-)

f.anthony.n.finch  <dot(_at_)dotat(_dot_)at>  -  I xn--zr8h 
Southwest Forties, Cromarty, Forth, Tyne, Dogger: Westerly or northwesterly,
becoming variable, 3 or 4. Slight or moderate. Showers. Good.

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