You can run a simple test to see if your ISP is blocking port 25. Open a command prompt for windows or for OS X and type in the commands below.

telnet 25


If your ISP is blocking port 25 you will not get a response back. However if it isn't blocking port 25 you will see an output similar to the one below.

[user@host:~]$ telnet 25
Connected to
Escape character is '^]'. ESMTP Exim 4.69 #1 Mon, 07 Jul 2008 00:22:59 -0600
220-We do not authorize the use of this system to transport unsolicited, 
220 and/or bulk e-mail.

Please keep in mind that you should be using a secure (SSL) connections for Outgoing SMTP and Incoming IMAP or POP3.

Outgoing SMTP Port 587, Incoming IMAP Port 143 and for Incoming POP3 port 110.

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