Can someone exlain the Port 587 change for me?

[M-]

This morning I was using Port 25 to send e-mail to outgoing.verizon.net, and it worked fine.  This afternoon it failed.  After navigating through menu heck, I found a technician who, after about 40 minutes, changed my outgoing port to 587 and everything worked.  I would love to know why things changed.  As far as I know there's no 3rd-party mail service involved, just my e-mail client (Thunderbird), which didn't change during the day, and my connection (ATT DSL -- I'm not at home, now), which also hasn't changed.  From reading the (now read-only) Port 25 Change threads, I see that port 587 might not work someday, either, and I'll have to go back to  port 25.  Is there any method to this madness?

And to those who simply say if I'm not happy, I should just switch to a different ISP, I will say I'd be happy to, if e-mail address portability becomes reality as cellphone-number portabiloity did.

[somegirl · Accepted solution]

If you are using outgoing.verizon,net on a Verizon connection, port 25 should always work. 587 will also work, but is not required.

You problem here is that AT&T has a similar block to the one Verizon has on their networks for port 25 with 3rd party email servers. So this issue is actually because you are using the AT&T connection, and has nothing to do with Verizon.

[M-]

Well, you can't beat service like that... you are Some Girl! It starts to make sense now, although I've got to do some more reading to see why 587 is inherently any more trustworthy than 25.  Thanks.