Mail sent to email@example.com gets bounced:
CONFIG_TEXT: postfix/pipe: 7B3F6346FBF0: firstname.lastname@example.org, relay=plesk_virtual, delay=0.01, delays=0/0/0/0.01, dsn=5.4.6, status=bounced (mail forwarding loop for email@example.com)
firstname.lastname@example.org is set to forward mail to email@example.com.
Mail sent to firstname.lastname@example.org gets forwarded to email@example.com. This causes loop and messages get discarded.
Turn off mail forwarding for one of mail addresses that are in the loop.