I use Office365 "Business essentials" for wormhole.network

It was surprisingly cheap and it includes other stuff like 1TB OneDrive and OWA is quite cool (even though I use Outlook or Mail, depending if I'm on my main computer or not).

I have only one inbox, but a few aliases, including some for a second custom domain. As far as I can tell I haven't been charged extra apart from what they advertise here: https://products.office.com/en-gb/business/office-365-busine...