I'm aware of reports of issues with mail delivery recently ... do not know if this is related or sheds any light on matters.
I have two domains on my account, a lot of mail boxes and catch all set.
All of the historical email addresses for my old business domain t*top.co.uk route via aliases to one mailbox. This evening I received two quarantine notifications in that mailbox reported to be sent to addresses never used with that domain AND NOT MATCHING AN ALIAS to that mailbox.
How can that happen - I would have expected such emails to go to the account's catch all mailbox.
From: "Email Alerting Service" <firstname.lastname@example.org>
Subject: Alert: An email addressed to you has been quarantined
Date: Mon, 30 Oct 2017 12:08:31 -0000
X-Mailer: Microsoft Outlook 16.0
'Lincoln@' is not an alias of the mail box t*top ... so how does it end up there and not in my default emailbox?