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The solution requires some modification to allow special case such as WebMail on the same server (WebMail sending emails without authentication).
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The solution requires some modification to allow special case such as WebMail on the same server (WebMail sending emails without authentication).

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My server host multiple domains, I have found some users sending spam, they login to SMTP using account 'user@domain.com' but sending email with SMTP FROM is name@gmail.com. How do I stop that emails?
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My server host multiple domains, I have found some users sending spam, they login to SMTP using account 'user@domain.com' but sending email with SMTP FROM is name@gmail.com. How do I stop that emails?

Exim - Stop user from sending email with fake FROM address

The Linux operating system, in all its flavors, has its own share of security flaws that allow intrusions, but there are various mechanisms by which these flaws can be removed, generally divided into two parts: authentication and access control. Authentication is responsible for ensuring that a user requesting access to the system is really the user with the account, while access control is responsible for controlling which resources each account has access to and what kind of access is permitted.