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Solution: Enable SMTP Authentication in your e-mail clientÂ
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Symptom: When sending messages out, the server repeatedly asks for your username & password, despite having entered the right ones
Cause: If you are sending out using the regular port 25, it is possible that your local Internet Provider is intercepting SMTP communications on port 25 and forcing you to use their own SMTP servers. Your SMTP credentials would thus fail against their servers
Solution: Change your outgoing SMTP server port to another value. You can use ports 26 or 587 for regular/TLS server or port 465 for SSL service.