Email from another domain (another tenant)?

[Brent Ellis]

I believe I know the answer to this, but figure I'll ask anyways:

I have 2 O365 tenants,  Tenant One has @domain1.com and Tenant Two has @domain2.com.

Is there a way to enable a user in Tenant Two (joe@domain2.com) to be able to send email as joe@domain1.com from their outlook without having 2 accounts (one in each domain)?

[#2]

Nope. Best you can do is verify a subdomain in the other tenant and use it to assign aliases and send messages. Or send via an external system, but make sure to take care of SPF/DKIM checks.