Review Board documentation mentions that
Sender Headers
Review Board can send e-mail on behalf of users. This may happen when creating a new review request or reviewing some code.
E-mails appear to be sent from the users, rather than from Review Board itself.
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By using these two fields instead of just faking the From address, we can avoid e-mails appearing to be spam or otherwise malicious. Many modern e-mail clients warn if the From address appears to be suspicious.
Is there any way to disable email sending on behalf of users? I want to send emails from default email which is set in the admin panel.