See above. To reproduce this bug, create [email protected] and [email protected] on your CyberPanel server. Set [email protected] to forward to [email protected]. If you send an email to the test1, test2 receives not one but two copies of that email. I found the fix! Add the following line to /etc/postfix/main.cf:
enable_original_recipient = no
After, you should no longer receive the duplicate emails.