I have multiple email accounts and domains, and I've come to like Spark; Using the free tier, and using its mobile app and MacOS variant.

It has one login that will give you access to all inboxes, maps etc. Also nice and easy switching between "regular viewing" and "smart views" that show your mail more organized.

Snoozing mails and planning mail sending is also very nice (send stuff in the morning to prevent people from thinking you respond at evenings also).