How does SMTP authentication work?


tacit
Asked:
2012-02-21 12:23 pm EST

Hits: 3,130
I asked a question this morning. Thank you for your reply. But my problem is as follows:

Suppose I own the domain 123.com and host it on inmotion shared hosting.

I set up 2 email address:
A@123.com
B@123.com

In order to send mail from A@123.com by SMTP, I need to login into Outgoing Mail Server: mail.123.com. This requires authentication. I can use A@123.com as user name and its mail password as password. The question is, after I login as A@123.com, why can I also send an email from B@123.com?

Thank you!!

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Tim S.
Staff
6,907 Points
2012-02-21 12:51 pm EST
Hi tacit,

Thanks for getting back to us. I'm more than happy to assist you today. SMTP authentication is there solely to validate that there is an account on the server thus providing access to send emails.

The from address is handled in the headers of the email and is not part of the SMTP protocol. SMTP authentication is designed to keep emails from openly being sent from a non-user account on the server. Once the account has been authenticated (when you log in), there's no other SMTP authentication that takes place.

You can send email from anyone after logging in. Who an email comes from is determined by the email headers, and SMTP Authentication does not scan email headers.

This is the same on virtually all email servers that use the SMTP protocol.

I hope this helps! If you need further assistance please feel free to contact us.

Thanks!

Tim S

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