Marking Quarantine Notice senders as safe for entire tenant

Definitely room for lots of subjectivity but I like to use Transport Rules for things like this (org-wide, system like stuff, such as quarantine notifications), and stick to the TABL for allows/blocks otherwise.  You could make a transport rule that when messages from that sender come in, it bypassed spam filtering (which will bypass the basic stuff, apart from things like URL reputation, file reputation, malware, and other high-confidence-by-default detection techs.  You can also use the same or another transport rule to make sure some messages are always in the Focused view for Focused Inbox users.