I have tried many mail apps but always came back to good old Apple mail, however the sandboxing of mail, especially searches means for me it is not exactly a good digital citizen any more when it comes to collaboration with other apps.
The Catalina update completely broke integration with Houdahspot and Busy Contacts so I have decided to go back to Mailmate which I used before and only really dropped because of the interface, it’s not pretty but insanely powerful.
This gives me Omnifocus as a task manger, Busy Contacts as a CRM and Houdahspot for saved and granular searches which turns the Mac filing system into the ultimate bucket app.
I may have sacrificed pretty for power but I will go with the power anytime.
Last piece in the puzzle may be Busy Contacts to give me dated notes cross referenced to contacts. Downside: Cost, these apps are not cheap plus I need to remote login to my Mac to use some of these on iPadOS, but I am rarely away from the a Mac for long enough for this to be an issue and I can always save notes in Drafts to be updated later.
What I have learnt is premium apps like Omnifocus Houdahspot and Mailmate pay for themselves many times over in function and reliability, and that never comes cheap. These rarely seem to be in favour with the cool kids, new and shiny no, proven and powerful yes, which would you prefer?