Is your ISP blocking outgoing port 25?

Michael Thomas mike at
Tue Jun 16 07:53:36 UTC 2009

Sean Donelan wrote:
> 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 work.
> 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 things.
Better yet would be for the MUA to probe for the "best" configuration. 
Setting up mail is a
royal PITA even if you know what you're doing. And a near death 
experience if you don't.


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