Generally if you are using a mail server apart from your ISP’s one, such as your web host, then you will need to enable SMTP Authentication on it to be able to send outgoing mail. When you try to send mail this will authenticate with the outgoing mail server, giving them your username and password for your email hosting that you are authorized to send mail from. Most servers will not accept mail if you do not authenticate with them, a server not requiring this would be a spammer’s dream and this mail server would soon get blacklisted by spam databases.

Here is how to enable SMTP Authentication in some common email clients: (more…)