Is your ISP blocking outgoing port 25?

Sean Donelan sean at
Fri Jun 19 22:24:23 UTC 2009

On Fri, 19 Jun 2009, Jeroen Wunnink wrote:
> 1. Customers remember it more easily
> 2. Some ISP's also block 587 (hence 'SMTP ports' rather then 'SMTP port' in 
> my previous comment ;-)

Those same clueless ISPs will probably block 2525 someday too, clueless 
expands to fill any void.  And using non-standard things like 2525 only 
lead to more confusion for customers later when they try someone else's 
non-standard choice, e.g. port 26 or 24 or 5252 and wonder why those don't 

On the other hand, why don't modern mail user agents and mail transfer 
agents come configured to use MSA port 587 by default for message 
submission instead of making customers remember anything? RFC 2476 was 
published over a decade ago, software developers should have caught up to 
it by now.  Imagine if the little box in Outlook and Exchange had the MSA 
port already filled in, and you only needed to change it for legacy 

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