Is your ISP blocking outgoing port 25?

J.D. Falk jdfalk-lists at
Thu Jun 18 20:36:58 UTC 2009

Joe Provo wrote:
> On Thu, Jun 18, 2009 at 03:36:44PM -0400, 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.
> Yes, it is standard practice for non-server accounts and most dynamic-only
> accounts; only allow unauthenticated smtp traffic to your own smtp servers.
> If you are not running server-to-server traffic at the end of that broadband
> pipe, then you should be shifting your userbase to authenticated on the SUBMIT
> port [587] anyway...

The Messaging Anti-Abuse Working Group (MAAWG) published recommendations for 
managing port 25 traffic a few years ago, and even then it had already been 
a widely-accepted best practice for nearly a decade.

J.D. Falk
Return Path Inc

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