I received an electronic notice (email message) from Verizon last week indicating that they will start blocking SMTP (TCP Port 25) on or around June 1, 2010 for all Verizon FiOS customers.
Their taking this action in hopes of stemming the flow of SPAM from infected home personal computers.
I’ve never heard of Mail Submission (TCP Port 587) before this announcement so I had to Google for it and do a little research. It looks to me like Mail Submission is just SMTP with authentication although I could be wrong, perhaps someone would help clarify the benefits of using TCP port 587 over 25.
In any event, if you are a Verizon FiOS subscriber and you use a regular email client you’ll probably need to make some configuration changes.
You can find the official Verizon announcement here.
The “Mail Submission” term is a throwback from when a MUA on a Unix workstation would submit mail to an MTA. The MTA, running on port 25, was used only for relaying mail. With modern PCs the line between MUA and MTA has been smeared.
There has been much discussion about different ports for SMTP on the NANOG list. My feeling is that the port number is not as important as authentication. IMO authentication will do more to reduce the amount of SPAM from zombie PCs, then simply changing the port number a server listens on.
One fault that I see with some ISPs is that they still allow unauthenticated SMTP from hosts within their network to their own SMTP servers. I’m not sure if this is the case with FiOS, since I do not use their mail servers.
Michael McNamara says
Thanks for the background information Chris!
I believe Verizon FiOS customers are required to authenticate when making a SMTP connection for the purpose of sending electronic mail.
I agree with you that I’m not convinced that this move will really help the SPAM problem much… although it’s sure to confuse and frustrate users.
Greg L says
I just ran into this same issue. Seems like a really stupid update.. Now it’s going to force me to use port 587 at home and then switch my laptop settings to use port 25 when I get to work EVERY DAY since I use a laptop!!! Very stupid..
Verizon didn’t think this through at all and consider laptop and mobile phone users (like the iPhone and the Droid) that jump onto WiFi when you’re at home to send e-mails. So now I’ve got to switch my settings to a non-standard setting every time I come home??? Really? :-(