If you’re able to receive email, but are having problems sending emails, you may need to check with your ISP to see if they have any restrictions or have recently implemented any filtering on their network in an effort to reduce spam and increase security.
Different ISPs use different methods. The information below may help, but keep in mind that ISPs sometimes change their tactics to try to keep ahead of spammers, so visit your ISP’s customer service section on their web site or call them to get the most up-to-date information.
Cable One, Qwest & Integra
Cable One, Qwest & Integra use Port 25 filtering, meaning that they block that port. Instead, when you’re using Cable One or Qwest’s or Integra’s Internet service and configuring your email client for POP3, you’ll need to change your email client to send email using port 587. If you move your computer to another location (say you have Qwest at home and Midcontinent at work), you’ll need to change your email client’s port setting every time you switch locations and want to send email.
Port 25 (preferred setting) or Port 465 (may not be compatible with all software/providers)