SMTP Authentication is the mechanism by which the clients of an ISP identify themselves to the mail server through which they intend to send email. It is not possible for any person to send email via any mail server they choose; mail servers will only allow the sending of email by legitimate users.
How it works:
Upon sending an email, the user’s mail client (Outlook, Outlook Express, Thunderbird, etc) will identify itself to the mail server by supplying the username and associated password of the email account. Should these credentials be valid, the user’s mail is accepted and will be processed and relayed to its recipient destination. If the authentication fails, an appropriate error message is generated by the user’s mail client.
View the Email setup guides section for detailed guides with visuals on how to setup or edit your email account using a specific email client software, for example Outlook.