Internet service providers (ISPs) are starting to block their customers from accessing port 25 on servers located elsewhere on the Internet. Port 25 is the default port used by SMTP. SMTP stands for Simple Mail Transfer Protocol, and is the protocol used to send email to any outgoing email server. This port is used by all outgoing e-mail servers, and email programs which send email such as Microsoft Outlook and Outlook Express. If you call them up and ask them why, they will tell you to use the mail server they provide to you and provide you with the instructions on how to use their outgoing email server.
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