Why SPF over PTR?

[Barry Margolin]

In article <cog674$ml9$1 at sf1.isc.org>, gregrjones at yahoo.com (Ludwig77) 
wrote:

> I must not be understanding SPF correctly because I don't understand
> why it is better for preventing sender domain forgeries than doing a
> simple PTR lookup.
> 
> Wouldn't a simple comparison of the sender's IP address to their
> domain name via a PTR record lookup be sufficient to check for
> forgeries? I realize that not everyone has PTR records, but more have
> PTR records than SPF records.
> 
> What am I missing?

Many organizations don't have their own mail servers, they relay through 
their ISPs' servers.  But they still want to use their own domain names.  
So you need some way to indicate that it's OK for mail.isp.net to send 
out mail from user at customer.com.

-- 
Barry Margolin, barmar at alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***