Originally Posted by torgnyw
Set mynetworks = 127.0.0.0/8, 192.168.1.0/24
My home network is 192.168.1.0 with netmask 255.255.255.0 (24 bit mask)
This worked fine for me. This setting sets what networks you allow to send mail trough your smtp server.
I understand this post is a bit too old but I would like to say thank you to Torgny as his/her post gave me an idea. I had exactly the same problem and what saved me was entering my ISP's IP for "mynetworks" and it started to work. I am not sure though but it looks like my ISP has some slightly misconfigured parts in their Postfix. Could anyone also comment on IP for "mynetworks", please? Thanks!