A company I support uses Office365/Exchange Online with email@example.com email addresses.
They're going to be changing their name, and as such have registered newcompany.com, and I've verified the domain within 365, etc.
I want to set it up so that emails to both user@new and user@old get to the right spot, and when they send emails, they come from user@new, but they can still log in to OWA or via Outlook using the user@old credentials they know and love.
I've tested on one user adding firstname.lastname@example.org as their primary SMTP address, but when you email as that user, it still comes from email@example.com.
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