Gmail

I've been on Gmail long enough that migrating would be a project in itself, and honestly it still works well. I use labels and filters aggressively to keep the inbox from becoming a dumping ground — most notifications and automated emails never touch the inbox at all. The search is still the best in the business.

I access it through the web on desktop and Apple Mail on iOS. The web interface has gotten progressively better over the years; I've stopped looking for alternatives because there's rarely a meaningful gain.