Re: Configuring a mail gateway

[Nikolaos Milas]

On 3/9/2011 11:09 μμ, Noel Jones wrote:

If we use:

    relay_recipient_maps =

(that is, empty) then *all* recipients for the hosted domains (those
listed in relay_domains) are accepted/forwarded?
Yes.  That turns you into a backscatter source, clogging your queue
with undeliverable mail and eventually getting you blacklisted.

Not recommended.

OK, I understand.

Is there a way we can configure the gateway server to ask the final
delivery server (as defined in /etc/postfix/transport) whether the
user is valid and decide to allow or reject the mail transfer? In
this way we don't have to maintain a list of recipients.

http://www.postfix.org/ADDRESS_VERIFICATION_README.html

This requires that the next-hop server reply with a 5xx response to
nonexistent recipients.

   smtpd_recipient_restrictions =
             permit_mynetworks, reject_unverified_recipient,
   reject_unauth_destination

and on the *final destination* (next hop) mail server:

   unverified_recipient_reject_code = 550

...??

I guess this is what you mean by "active recipient verification". Right?

Thanks again,
Nick

So, in order to implement such a solution, would it be sufficient to do something like the following, on the *gateway* mail server:

smime.p7s
Description: S/MIME Cryptographic Signature