Can a guest account (different O365 tenant), have a mailbox/SMTP address in another tenant?

[exigenttechguru]

We have O365 and several of our business partners send email to clients on our behalf using a mailbox within our tenant (each is a user in our tenant). Several of these users have their own O365 account/tenant and I'm wondering if there is a way to give them a mailbox, but using a guest account (soandso@othercompany.com) as the user while still having an internal SMTP address for messages sent/received via our mailbox? If they were to be disabled by their own company, the guest account would be deactivated and the access to the mailbox we host for them would be essentially disabled as well. The goal is to maintain a single source of identity even if the user is not one of our own, but still requires access to resources we provide. Thanks in advance!

[#2]

Technically, yes, I've played with this scenario a while back: https://www.michev.info/Blog/Post/2256/some-new-interesting-experiences-with-guest-users-in-office-3...

I wouldn't recommend it though. There's no official statement from Microsoft that this is supported, so you can expect the occasional issue. For starters, you will have to unhide it  Moreover, since a mailbox requires a license, you can just create a regular user account and provision a mailbox for it. But it's up to you really.

[#3]

@Vasil Michev, thanks for that article reference. Very interesting indeed... As noted, the goal was more focused on allowing us to trust those third parties to manage their identity. We've had one or two occasions where a third-party staff member was terminated but we were not informed for days or weeks. If we'd been using their true tenant user account as a guest, they'd have been disabled as soon as their company disabled them (yes, I realize there could still be some risk here). I'm interested to see how MS continues to develop their guest functionality as it relates to O365. Thanks for the quick response!

[#4]

@exigenttechguru  we have a similar requirement. Did you manage to find a solution.