If you are having problems with sending POP3 email (SMTP or Outgoing Email), there are a few things you can do. Usually one of the following will remedy the situation:
1. Change the outgoing port to 26. Port 25 is the default but it is sometimes blocked by ISP's because it can be used for sending spam email. Changing to 26 can immediately allow email to be sent.
2. Your ISP may require you to use their SMTP server for outgoing mail (instead of mail.yourdomain.com). However, some ISPs will allow you to use mail.example.com with port 26. Simply, if port 26 doesn't do anything, check with your ISP if you must use their SMTP server for outgoing email instead of your own.
3. Check the email scanning settings on your firewall/anti-virus software. If it's set to scan all outgoing email before sending it, you can run into problems and it will prevent all email from leaving your computer. Usually changing the settings or turning it off will remedy the problem.
4. Double check all pertinent settings are entered correctly such as your username (full email), domain name, email address, and password. A simple mistake of 'stmp' instead of 'smtp' will cause an error.
5. Access command line:
Using Windows: Click Start -> Run, and then type in CMD
Using a Mac: use the Terminal application in the Applications/Utilities folder.
Now, type in TELNET example.com 26
(replace example.com with your actual domain name, without the 'www' part).
If you see this message, you can connect to the server and the problem is most likely related to how the email program is setup:
220-servername.host.com ESMTP Exim 4.34 #1 Fri, 02 Nov 2012 09:04:22 -0600
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.
If you see some other message, copy and paste that message and contact us for assistance.