Is your ISP blocking outgoing port 25?

Charles Wyble charles at thewybles.com
Thu Jun 18 14:52:45 CDT 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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