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I have a Mail server (FQDN: mail.ours.com) using Postfix and Dovecot, users having email address like [email protected]. Like many others SMTP server, if user claim that they are from @ours.com, they need to pass sasl or should be in mynetwork parameter according to the restriction setting; so if user do not pass sasl and not having the ip address in mynetwork, they may got some error message like “sender not login”.

The situation is when a user [email protected] want to send email to [email protected], but Bob do the setting to let his email forward to [email protected]. So SMTP server from external.com will interact with ours SMTP server and claim that the sender is from [email protected] wanted to send mail to [email protected]. After the request, SMTP from external.com will receive the error message from ours SMTP server said that “([email protected]) sender not login”, and Amy will finally got this bounce error message.

I have no idea how to deal with this situation, very appreciate if anyone can give me the solution or leave some comment, thanks.

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    I have never encountered a mail server that was configured in that way. It looks like you are trying to (poorly) reinvent SPF/DKIM...
    – fkraiem
    Mar 19, 2019 at 4:24
  • Thanks for the comment, can you kindly tell me more detail about your reply. I'm not trying to block any client from our mail server, i think it's reasonable to reject someone who claim that he is valid user in our mail domain but cannot prove his identity. (Because mail server from external.com cannot prove that she is [email protected], so our mail server reject the request with "sender not login", but if she is [email protected], everything will be fine), thanks again for the reply! Mar 19, 2019 at 8:25
  • That's exactly what DKIM is for; look into it.
    – fkraiem
    Mar 19, 2019 at 8:28
  • Thanks again for the comment, but DKIM seem not work for the situation I encounter. Below is the process 1. [email protected] want to send email to [email protected] 2. BOB([email protected]) "forward" the mail to [email protected] 3. external SMTP server make the request to ours SMTP server (MAIL FROM: [email protected], RCPT TO: [email protected]) 4. ours SMTP server reject the request according to the setting(reject_sender_login_mismatch in smtpd_sender_restrictions) with Error Message(<[email protected]> sender not login) How can I accept this request make by external SMTP server. Very Thanks! Apr 14, 2019 at 12:46
  • The point is that since the mail would be properly DKIM-signed, your server should accept it regardless of where it comes from. smtp_server_restrictions is not the proper mechanism for what you are trying to do.
    – fkraiem
    Apr 14, 2019 at 13:27

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