I have been getting this lately and I have not been send them out. Can some please have a look at it.
Reporting-MTA: dns; web-atmail2.tpgi.com.au
Arrival-Date: Mon, 31 Aug 2020 23:39:20 +1000
Final-Recipient: RFC822; firstname.lastname@example.org
Remote-MTA: DNS; us-smtp-inbound-1.mimecast.com
Diagnostic-Code: SMTP; 550 Invalid Recipient - https://community.mimecast.com/docs/DOC-1369#550 [u8UdtEc_Mdqx6cbJ4CelZw.us217]
Last-Attempt-Date: Tue, 1 Sep 2020 00:11:52 +1000