I have been setting up a mail server of which smtp is an integral part. I could access it through my old net connection at home and I can through work but I am currently staying somewhere with Optus Cable. They block port 25! I called their tech support to confirm, he did say it was possible to have to port re-opened for this individual connection. But I am not the account holder. whirlpool forums also suggest an online method of removing the block.

So my advice to people in a similar predicament is to use the tools provided by zoneedit.com I can only hope you find this before wasting too much time like me.

Here is a handy list of Optus’ other blocked ports:

25 SMTP 80 http 135 – windows RPC worm/exploit 13 [789] windows file sharing/netbios 16 [01] snmp 445 windows 2k/xp filesharing 593 RPC as 135 1080 socks src: whirlpool