Gordon Dexter on 26 Aug 2009 10:19:02 -0700

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Re: [PLUG] Verizon blocking port 25

Basically the purpose of port 587 is to distinguish between traffic between mail servers and traffic from an end-user client (e.g. thunderbird) and a mail server.  Port 587, at least in theory, always requires a username and password to submit email, whereas servers running on port 25 don't necessarily, so it can be used to send spam more easily.

Honestly if it's possible I'd just switch everything to SSL.  That uses a port that Verizon won't block, and makes all your traffic more secure besides.  If that's not possible, just run your server on port 587, have everybody use that port instead, and make sure to require authentication.


On Wed, Aug 26, 2009 at 1:06 PM, Greg Helledy <gregsonh@gra-inc.com> wrote:
Verizon will soon be blocking outgoing connections on port 25 for
dynamic IP customers.  This is presented as an anti-spam measure.  Their
instructions are to change the port in your SMTP client software to port
587 (which they presumably redirect to 25 before passing the packets on?)

Obviously this is a PITA for our laptop-using employees because they
need to use port 587 when on the Verizon network and 25 elsewhere.  What
exactly is Verizon achieving by doing this that they could not do on
port 25?  Hope that no virus writers are clever enough to code to try
multiple known SMTP ports?



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