On January 22, 2010 at 16:26, Ken Hornstein wrote:
The port 25 block is pretty much standard for large ISPs today; it's
to prevent spammers from using massive networks of compromised PCs to
deliver spam.
Changing ports is useless unless authentication is required.
If deterring spammers is the primary goal, then ISPs can just require
authentication for customers over the standard SMTP port.
Changing to the submission port provides no benefit unless
authentication is required since spammers just tweek things to use
the submission port to send spam.
However, even with authentication, if a system is zombied, probably
would not take much for authentication credentials to be stolen by
the malware and used for sending out spam.
--ewh
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