Simple Python script as SMTP server for outgoing e-mails?

[Gilles]

On Sun, 21 Jul 2013 21:01:09 +0000 (UTC), Grant Edwards
<invalid at invalid.invalid> wrote:
>Unless you've got a static IP address, a domain name, and a valid MX
>record that will match up when they do a reverse DNS lookup, it's
>pretty unlikely that you're going to have much luck running an SMTP
>server.  Most other SMTP servers are probably going to ignore or
>reject your attempts to transfer mail from your own SMTP server.

Incidently, how do ISP MTAs find whether the remote MTA is legit or
running on some regular user's computer?

1. Query Reverse DNS for IP
2. Find domain
3. Query DNS for MX
4. ?