It is becoming more common that ISPs are blocking port 25 (SMTP port) forcing you to use their SMTP server. To see if you are blocked:
(a) Click Start Button (Windows Desktop)
(b) Click Run
(c) Enter "telnet"
(d) Enter "open mail.domain.com:25"
If you see a message like: 220 www.domain.com ESMTP Then you are not blocked. If you can't connect, you are blocked. You should change your port to 26.
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