Nginx mail proxy - ensure sender match authenticated user

[mbrother]

Hello Maxim,

Thank you for your answer. As you know, nginx does not send Auth command to
backend server, so there's no way for the backend to know if the sender
matches the authenticated account. I tried proxy_smtp_auth config but nginx
send mail COMMAND to my server but it can not understand :(

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,291574,291583#msg-291583