You might receive an email with the subject title ST0RAGE QU0TA LIMIT EXCEEDED; Retreive your (47) New Pending Messages ✉ !!! On Hold with a link in as follows:
This is a fairly common trick and one that should not be catching you out. A simple way to block these in Office 365 or MS Exchange is as below:
Office 365 - block attachments with extensions containing these text patterns:
Microsoft Exchange, block attachments with these text patterns in their extensions: