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Thank you @anold, If can, would you give me a sample configuration.
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Thank you @anold, If can, would you give me a sample configuration.

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The difficulty as described in the faq deals with controlling inbound by those restrictions. The option you seek on enforcing outgoing sender domain is not enforceable once the connection is set to allow relay.
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The difficulty as described in the faq deals with controlling inbound by those restrictions. The option you seek on enforcing outgoing sender domain is not enforceable once the connection is set to allow relay.

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not a perfect solution, but ca give me some clues
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not a perfect solution, but ca give me some clues

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I configured a Postfix &amp;&nbsp;Dovecot mail server to send notification to user. I want to restrict email address domain to prevent user from send out email with fake email address.<br />
Example: my domain is <b>truedomain.com</b>, so I want only email address with this domain can be send out via my mail server. Other fake email address are not able to send out.
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I configured a Postfix & Dovecot mail server to send notification to user. I want to restrict email address domain to prevent user from send out email with fake email address.
Example: my domain is truedomain.com, so I want only email address with this domain can be send out via my mail server. Other fake email address are not able to send out.

How to restrict Email send out to  with Postfix to prevent user from using fake address?

Within Internet message handling services (MHS), a message transfer agent or mail transfer agent (MTA) or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture. A MTA implements both the client (sending) and server (receiving) portions of the Simple Mail Transfer Protocol (SMTP). The terms mail server, mail exchanger, and MX host may also refer to a computer performing the MTA function. The Domain Name System (DNS) associates a mail server to a domain with mail exchanger (MX) resource records containing the domain name of a host providing MTA services.

Email Servers

An email client, email reader or more formally mail user agent (MUA) is a computer program used to access and manage a user's email. A web application that provides message management, composition, and reception functions is sometimes also considered an email client, but more commonly referred to as webmail.