I outsource all my domains email to FastMail.com because their a good price, and they have an easy interface. I get 25 GB of storage on the $50 a year standard plan. I can have pretty much unlimited (100) domains connected to my one user. Plus unlimited aliases (well, almost unlimited, 600). Good solid IMAP performance and speed. I really like that I can secure my FastMail.com account with two factor authentication, and use app passwords. I can also delegate whether or not an app has access to email, calendar, contacts or all of the above. A cool thing is, I can access the FastMail.com web mail interface from my domain without me needing to setup a web server. Sort of like this: https://mail.########.net and you visit that link, and presto you have your very own login page. You can even customize it, I believe. Go to their site here at FastMail.com
Check them out, and see if they will work out for you.
Sign up for Fastmail at this page here: FastMail.com