The Simple Mail Transfer Protocol (SMTP) is used to send emails from one server to another. When configuring an email client or server, you may need to choose which SMTP port to use.

Here are some guidelines to help you choose the right SMTP port:

• If you are using a secure connection (TLS or SSL), you should use port 587 or 465.
• If you are using an unsecured connection, you should use port 25.
• Some ISPs block port 25 to prevent spam, so if you are having trouble sending emails, you may need to use a different port. In this case, you can try using port 587 or 465.
• If you are using a local email client (such as Microsoft Outlook or Apple Mail), you may need to use a different port depending on your network configuration. In this case, you should consult your network administrator or ISP for more information.