On Tue, Jan 29, 2013 at 12:22:35PM +0100, M. Fioretti wrote:
> of course, any comment on this is still welcome, as well as on any
> weakness in my server postconf -n output.

The original issue was to be able to relay from a dynamic residential 
IP address on your server. Your solution, adding the dynamic IP to 
mynetworks, is less than ideal in many ways. For one thing, it's a 
high-maintenance solution, where you must change mynetworks with 
every IP address change. For another, what if you don't get to it? 
What if the new owner of your previous IP address is running malware 
with an open relay tester? What if that malware finds you? Ouch!

The standard solution is SASL AUTH (typically also requiring TLS 
encryption for security.) This is covered here:

http://www.postfix.org/SOHO_README.html#client_sasl_enable

A less common, but very good, solution is TLS authentication, which 
is covered here:

http://www.postfix.org/TLS_README.html#server_access

If you don't want to get into all that, you can use a VPN like 
openvpn to make a tunnel through which to send your mail, and add 
your tunnel IP address to mynetworks.
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