ISP port blocking practice

Fri Oct 23 00:45:56 UTC 2009

Sean Donelan wrote:
> On Thu, 22 Oct 2009, Lyndon Nerenberg (VE6BBM/VE7TFX) wrote:
>> My experience is that port 587 isn't used because ISPs block it
>> out-of-hand.  Or in the case of Rogers in (at least) Vancouver, hijack
>> it with a proxy that filters out the AUTH parts of the EHLO response,
>> making the whole point of using the submission service ...  pointless.
> 
> You mentioned this last June.  Can anyone else corroborate it?  Rogers 
> says they don't do that, and lots of other people seem to be able to
> use port 587 on Rogers (and other ISPs) without problems.
> 
> All the cases I've looked at, where someone claimed an ISP was blocking 
> port 587, it turned out to be some other problem.  The most common 
> reason was related to some security software/host based firewall running 
> on the user's own computer.

First thing to check when "email is stuck in my outbox"
Next is to check whether outlook is trying to do SMTPS on 587 instead of 
STARTTLS. Hence 465 SMTPS port workaround.