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Re: Anti-recommendation: Comcast.

 Bill Horne wrote: 
> Checking for PTR records is routine for most ISP's... 

I'm referring to not just checking for the presence of a PTR record, but 
applying a regular expression to the format of the returned PTR record. 
This I consider arbitrary, and highly error prone. 

The idea of tracking blocks of dynamic IP addresses is also tenuous 
(unless the ISPs themselves participate in the system), but a step more 
reliable than making judgments on the appearance of the PTR record. 

> ...and I'm surprised that you haven't gotten rejections more often. 

Pretty much never...though of course many spam rejections don't generate 
a bounce. 

> Of course, it's imperfect - effectively, just a confirmation that the 
> machine sending the mail is not a desktop - but it's all we've got. 

This classic web page provides a good rant on why most anti-spam 
techniques are fundamentally broken: 

No anti-UBM measure for SMTP-based Internet mail works

It has a section specifically on the above issue titled "Treating other 
ISPs' customers as third-class citizens." 

As a community who frequently chooses to operate our own servers, we 
should be doing our part to discourage these types of broad based and 
misguided anti-spam measures. 


Tom Metro 
Venture Logic, Newton, MA, USA 
"Enterprise solutions through open source." 
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