Increased Spam filters, Spyware/Internet Scanners, and ISP filters seem to be the major causes of email trouble tickets.
The number one problem I get is “I can receive email but I can’t send.” This usually follows my question, “Who is your Internet Service Provider?” Majority of ISPs are blocking 3rd party SMTP (TCP Port 25) in an attempt to prevent spam from their networks.
Here is a quick test to see if this is the case. Open up a DOS/Command prompt and type in:
telnet mail.domain.com 25 (be sure to replace domain.com with your own domain name)
If you see a black screen then you are being blocked.
Users can change the default port 25 to port 26 to solve this problem. We open an alternate port for Cpanel customers that run into this problem.
I have also found that Norton Internet Suite or any similar software, when configured incorrectly, can block mail traffic. When sending out mail, users may click the “block” or “Don’t Allow” button by accident and that will end your SMTP session prematurely. Be sure to read these security popup boxes carefully so that you don’t block legitimate traffic.
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Canadian Web Hosting