From: /dev/rob0 (rob0gmx.co.uk)
Date: Thu Feb 17 2005 - 18:18:32 CST

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On Wednesday 16 February 2005 13:02, Lars Weste wrote:
> I'm wondering how i can set up postfix to relay mails from trusted
> users with a dynamic address without open postfix as a spam relay? Is
> there a way without authentication, that i say any mail from domain
> mydomain.com to anywhere is allowed?

I set this up in association with my dynamic DNS service. Clients
register with my DNS service using a wget'able HTTP form. The backend
script for the HTTP form edits /etc/hosts in addition to running
nsupdate(8).

Postfix uses /etc/hosts in place of reverse DNS, so my access(5) table
with this line:
    .dynamic.mydomain OK
allows selected DDNS clients to relay. Of course this offer is void
where taxed or prohibited, or where nsswitch.conf(5) does not use
"files" before "dns" on the "hosts:" line, or perhaps in non-glibc
resolver routines that I wouldn't know about.

You don't need to run a DDNS service to set something like this up. For
SMTP relaying all you need to do is edit /etc/hosts. If you're really
concerned about security, like network sniffing, you could use HTTPS,
but plain HTTP was good enough for my personal comfort level for this.
Legitimate clients are happy and spammers are not relaying.
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