SymptomsParallels Plesk Panel version 9.x is running and Postfix MTA is used.
If message is sent to the full mailbox, not informative bounce message is sent to the recipient. Recipient will receive bounce message with the error: "Message can't be delivered".
But actually, message was not delivered cause mailbox quota is exceeded.
ResolutionIssue was discovered in Parallels Plesk Panel 9.x.
Bounce message for mailbox with exceeded limit is fixed in hotfix. Hotfix can be applied on Parallels Plesk Panel 9.x .
For applying hotfix replace the file $PLESK_LIBEXEC_DIR/postfix-local with the appropriate file from the attachment.
Please read article #8083 about a hot-fix installation procedure.