Is your ISP blocking outgoing port 25?

Charles Wyble charles at
Thu Jun 18 19:52:45 UTC 2009

Zhiyun Qian wrote:
> It has been long heard that many ISPs block outgoing port 25 for the purpose
> of reducing spam originated from their network.

Well blocking or redirecting to there servers, which have an 
undocumented filtering policy. All one needs to do in order to bypass 
that is use a vpn. Something lightweight like n2n could be used by the 
bot herders of the world.

I worked for a company that sent out several hundred thousand messages 
per day (an online card/invitations company). We ran spam assassian on 
our outbound farm, to prevent folks from using us to send spam. I 
presume the large service providers do the same.

> AT&T is the major one that I know of that is still enforcing this policy.
> But they said they can unblock port 25 upon request. I am not sure how easy
> it is.

It's trivial. A web form. You get the link when you try to send mail to 
port 25 anywhere else. At least with Yahoo/SBC dsl.

I got the business class DSL from AT&T and no such nonsense exists.

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