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

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, 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.
Sida SayInfrastructure EngineerAsked:
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arnoldConnect With a Mentor Commented:
You would need to setup a rule dealing with allow relay section where you would need to

Though have to double check how you would deny the sender given the user authenticated earlier or the IP is authorized to relay.

There is also the reject for SMTP of unknown domains.

It might be a combination, but it might be more complicated dealing with revoking relay rights, though mailing to an internal recipient might involve further research.  

Searching for postfix deny based on sender, reveals options/sites that can not be included here.
Sida SayInfrastructure EngineerAuthor Commented:
Thank you @anold, If can, would you give me a sample configuration.
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.
Sida SayInfrastructure EngineerAuthor Commented:
not a perfect solution, but ca give me some clues
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