iptables and netstat output are fine, postfix is listening on all network interfaces on port 25 and 587 and it is not blocked by a local firewall.
The dns record seems to be fine as well.
I then tested if I'am able to connect to your server on port 25 or 587 from outside but that not possible. I then tested the same for port 80 (apache) and this works.
So it seems that somehow the email ports are blocked between the internet and the server.
As you mentioned that this setup worked before, do you remember anything that happened right before the problems started that might be realted to the issue, e.g. did you configure something in the router or did youraccess provider announced any changes in ther service?