We're in the process of moving a lot of users from a cPanel-based email server (dovecot server). Since cPanel-based email server does not support email aliases, multiple user accounts were created for the same person.
So, for example, John Doe had: firstname.lastname@example.org, email@example.com and firstname.lastname@example.org. (Please don't ask me why they needed that many! lol)
Now, we'll be doing a mass transfer of all the email accounts from the dovecot server to Office 365/Exchange Online. So, each email will have a new account in Office 365. However, after the transfer we would like to merge all the email addresses for the same person, along with their emails, contacts and calendars, and then assign aliases.
How can this merging be achieved? (without using Outlook 2016 to copy each email account's mail box)