Ability to sort the conversations list by sender or "from" address. This is something that is able to be done today in Outlook, and can be key to certain users' workflows.
Instead of "From 9 to 5 from Mon to Fri", be able to say "From 9 to 5 from Mon to Fri, except on Dec 25, Jan 1, etc". This allows to take plan for holidays, teammate PTOs, company events, etc.