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What is SMTP-AUTH?

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What is SMTP-AUTH?  And why is it required on 3Essentials hosting services to send mail?


In order to protect 3Essentials servers and network from being used by spammers, 3Essentials requires SMTP-auth to be enabled on any method it's customers use to send mail.  There are basically two methods for sending mail:

  • from a mail client, like Outlook, Outlook Express, a webmail tool, etc.
  • from your website code, i.e., a webform in PHP, ASP,, etc. that collects information from a visitor, and sends an email to you with it.

Before spammers, providers and mail server administrators did not require you to authenticate to a mail server before you sent an email via one of these methods... you could simply connect to the server via SMTP, and send the mail.  But with the pervasive and intrusive nature of spammers, they've exploited this... and now any mail server that allows you to connect "unauthenticated" (i.e., not identifying who your are, and being authorized to send mail), is considered an "open-relay" for mail, and open-relays are a dirty word in the hosting business.

The best first line of defense is to require all people who send mail from your server to have a predefined username and password, and to use that when making the connection to the mail server.  This is SMTP-auth... an SMTP connection which requires "authentication" of your user id / pw before sending mail.  Each method for sending mail implements this slightly differently:

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