Outlook. Office 365, Gmail, and iCloud. I use multiple accounts and pick one I feel fit for each occasion, and to spread out spam emails or junk mails a bit. Office 365 is for a lot of things though, as it is an enterprise level mailbox and I pay $12.50/mo for also office apps and some other services.
One cool thing about office 365 or outlook is the rules work great. Apple Mail on Mac does not support any rules well, and tend to miss sometimes. I use the rules to move emails from specific senders to a unique folder so that inbox is a lot less cluttered.