Office 365 with Multiple Domains

Q: (from Jason)

Is there a limit to how many Domains that can be added to an Office 365 account?  As long as we own a domain, can we just keep on adding domains, or is there a limit?  Is it based on subscription?  Licenses? 

Secondly, if we wanted to use several domains for email, do we just need an Exchange Online license per email account, regardless of different domains?

For example, if we had 3 email accounts “@bkbusiness.com” and 2 other email accounts “@businessbk.com”, would we just need 5 Exchange Online licenses to make that work?

Microsoft charges by the mailbox.  That means you could have 2 or more email addresses/aliases pointing to a mailbox, correct? We could receive emails from 2 different aliases/email addresses to the same mailbox, but can we also send emails from both addresses?

For example, jason@businessA.com, and jason@businessB.com.  We could have both email addresses pointing to 1 mailbox, and we could send email from both email addresses, correct?

A: (including contributions from Shawn, Tim, and Michael)

As far as I know, there isn’t a limit to the number of domains that can be associated with an Office 365 subscription. I’ve since learned (thanks to Tim and Michael) that there is a TechNet article that indicates 600 (https://technet.microsoft.com/en-us/library/jj819265.aspx) I currently have three custom domains affiliated with my Office 365 subscription. And for each mailbox subscription, there can be as many email aliases as you want. Between my wife and I we have at least eight email aliases across the two users and three domains. When in Outlook, you can use the From button to specify which alias the message will come from.

  Steve