I have PuTTY installed on Vista. When I set it to Telnet and put in a host name of SMTP2Go.com and port of 25 the window opens for a second not showing any text then closes. I also tried ports 2525, 587, and 8025, which SMTP2Go says also work with the same result. I use Telnet from the command prompt (which I had to enable from the control panel) to open smtp2go.com with port 25 and it works. I also can use both PuTTY and the other Telnet to connect to outgoing.verizon.net. I am using Frontier for my ISP and it says on their site that port 25 is blocked, and other people have confirmed this, so I find it strange that I can access SMTP2Go on port 25 using Microsoft Telnet. Could SMTP2Go determine what client I'm using and block certain ones?
Also in Microsoft Telnet there aren't line breaks between my commands and the server's response with Verizon, but with PuTTY there are.