+1 for Fastmail.

I’ve been using it for about 3 years. I’m on the Standard plan (middle tier). It’s $4.20/mo. per user when prepaying for 3 years and ranges up to $5.40/mo. for monthly billing.

Not sure if there’s a (practical) limit on domains or aliases, but I have 7 domains and a few aliases plus a wildcard. Includes 30GB of storage per user.