Confusions about Email hosting using Office 365

Hello, I need Office 365 primarily for email hosting for multiple domains. The second use case is OneDrive storage.

365 plans include Exchange service, but it's not mentioned how many domains I can add and how many mailboxes I can create per domain.

Also, if I go to the dedicated page for Exchange, it shows pricing for each user. So I assume each user means each domain, which is really costly.

Please help me understand this. I made some Google searches, and people's answers confused me even more.

Thank you

Last company I worked for, we were paying monthly fees per user indeed. Each user could install the apps on 5 different devices tho.

perrymason said:

Last company I worked for, we were paying monthly fees per user indeed. Each user could install the apps on 5 different devices tho.

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This does not answer my question buddy

From what I understand it's 1 user = 1 domain = 1 mailbox.
Also, for personalized email address's, you have to buy from GoDaddy:
"If you don't already own a domain, you'll need to purchase a new one from GoDaddy. New domains typically cost between $5 and $25 per year. You will pay for your domain directly with GoDaddy."

I looked at Microsoft 365 Family, which says it's for up to 6 people, but it's still 1 mailbox.

Hosted Exchange is what you are looking for, and you pay per email account on a domain.

BuildMoreLinks said:

Hosted Exchange is what you are looking for, and you pay per email account on a domain.

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The base plan of Microsoft 365 is cheaper than the base plan of Exchange. And both charge per email account. Why should I buy Exchange then?