Linux email server for a small business

I have a small business that needed a self hosted mail server.

I've already planned for this server to be hosted on a VPS, and I already have a domain name. Now I just need a mail server that do what I need.

I need it to have:

A web interface

Be able to easily create new accounts/users from the web interface

Be able to create account/user without having to create a user on the server itself (optional)

I've been looking into PostFix, Mailcow and Mail-in-a-box, but I'm not quite sure about them.

Thanks a bunch.