[ShadowAce]

ISP's blocking 25 is a stupid solution.

I think so too--if you are running a mail server, that mail server can use any port it wants to. There's nothing magical about port 25.

[TalonDJ]

Exactly! The server can send OUT any port it wants to. Advocating blocking 25 demonstrates a lack of understanding or internet protocols and packet structure.

[N3WBI3]

I think its an ill advised (not a stupid) solution. So long as I can opt-in (with no extra charge) to having port 25 open I dont see a huge problem with it. Now if they touch 23, ill start the revolution...

[Squawk 8888]

What they're talking about is blocking outgoing traffic that attempts to connect to port 25 on any server outside the ISP's network. That would effectively shut down the zombies because all mail servers listen on port 25 for incoming mail.

My problem with this is that it would be a major PITA for anyone who operates his own sever (for mailing lists or whatever). Instead of blocking port 25, I'd rather have my ISP use the Open Relay Database and other blacklists to block traffic coming from known zombie or spambot servers. The reverse DNS lookup is also effective against spam with forged headers- in my company this technique alone shuts out well over half the junk.