Authenticating E-Mail allows the client to show the receiving server that this client has permission to relay e-mail through this sending server.
Types of Authentication for sending mail.
1) Authenticated Process (SMTP Authentication)
2) Non-Authenticated Process (User Authentication)
It is the most common method of sending E-mail. There is no verification done when relaying email.
Process of sending Email through Non-Smtp process must be disabled on servers(mail function) as it may lead to spamming via injected scripts in websites by Hackers.
Hacker can insert Simple PHP Script
<?php mail($to,$subject,$message); ?>
to send mail from your website where
$to-> can be list of mails.
$subject-> is subject of mail
$message-> Message to be send
Here no authentication will required to send Email, and they will will be delivered successfully to all Valid email Id’s.
This can cause IP Blacklisting of Mail Server, which results Email Delivery to Fail or Emails to be Marked as Spam and being delivered in Spam Folder for all the mails that are being sent from Blacklisted Mail Server whether they are authenticated or not authenticated.
If Email is not sent through SMTP authentication then it will almost always be flagged as spam .
One of the most common Non-Smtp Function is mail() in PHP.
SMTP authentication allows the client to show the receiving server that this client has permission to relay e-mail through this sending server.
SMTP log in to an actual account on a mailserver and send the mail through SMTP to another mail server. If the mail server is configured correctly, your mails are sent from an actual account on a mailserver and will not wind up flagged as spam.
It is the best way to send an Email. Many applications too use this process to send Email like Outlook, Gmail App and Many others.
Below are the links of code, to send Email from Website, through Authenticated process.