A few months ago I did a lot of research related to this. For example, Azure does not include email with their shared hosting plans. I intend to switch to a different host that also does not offer email hosting.
One thing to understand is that most email-only plans (such as Microsoft Exchange Online) that claim to support many email accounts provide just one mailbox for all the email addresses. I am not sure how to explain that but that was a deal-breaker for me. I want my email accounts to be separate.
I know I considered Zoho and decided it would not work for me; I don’t remember if it provides just one mailbox but if so then that is why I decided it is not for me. I know that I need more than 7 email accounts so $2 per account gets expensive for more than 10 accounts.
I tried 1and1.com but I could not figure out how to use an external domain; domains not registered with them. So I canceled it and got a call from a salesperson that said I could use a hosting plan even if I onlyu used the email services. Well I finally discovered that external domains can be added the same way as if we want to transfer registration to 1and1. It is a scary process (unless they have changed it recently) since we must answer all the questions as if we want to actually transfer registration. So I had it all set up but since my DNS only pointed to 1and1 for email they dropped the external domain from their system. I complained and they said they were going to fix the problem but I have not tried again. So as it happens, it is probably possible to use the 1and1.com email-only plan.
Look at 25 Mail St.. It offers 2 mailboxes for 5 and .50 per additional mailbox and multiple domains. I have not tried them but I intend to.