Re: [IMail Forum] AT&T blocking SMTP port?

[Len Conrad]

>Out of curiosity, why would they be  blocking
>access to someone else's SMTP server?

Hi Hugo,

A common spamming technique is for some @asshole to get on the net via a 
dial-up line (or DSL line, or cable connection) with ISP A and then start 
sending spam directly to mail servers everywhere else, undetected by ISP 
A.  ISP A gets attacked by other ISP's and spam victims as being the source 
of spam.

www.mail-abuse.org explains this very well, and maintains a world-wide 
database called DUL, Dial Up Lines, which contains the ip blocks of dial up 
lines.

For example, my IMGate in Paris is subscribed to DUL and it caught a dial 
up user from a Parisian internet/cable user, plus another dial-up in Korea.

When ISP's block SMTP traffic from their dial up ip's any ip address other 
than the other ISP's mail servers, the ISP are pre-empting being accused of 
and having to deal with spam originating from their ip blocks.

Len

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