Copying of the existing mail store:
In the case where the user already has email in Outlook downloaded via POP .. I create a new outlook profile for Office 365 and then import their email from the previous profile PST.
I’ve also used the Office365 migration CSV import to bring IMAP folders over in the case where the user was using a web based interface. Visit https://outlook.office365.com/ecp/?rfr=Admin_o365&exsvurl=1 and click recipients on the left and then Migration along the top. Sadly webmail address books are not so easy and need to be done manually.
To allow Office 365 to co-exist with your existing email service:
Then click Mail Flow on the left.
Click accepted domains
Double click on your main domain name (not the .onmicrosoft one).
Change the domain status to:
—Internal Relay: Email is delivered to recipients in this Exchange organization or relayed to an email server at another physical or logical location.–
This allows sent mail from O365 to users that are not yet on O365 to still be sent onto your existing email provider. If you don’t set this then users who have been migrated can’t send email to your legacy users and will get an invalid address bounce back.
To migrate a user:
Create them on O365. Select their username as <whatever>@yournormaldomain.com not the .onmicrosoft address you have in the list!
Copy all their email over and be sure you have it all!
Either set the forward on the mailbox to automatically forward email to the users “onmicrosoft.com” address _or_ delete the mailbox on and then add an Alias with the old email address and add an External Email Address to it.
For example I added Alias test
Then added an external email address of firstname.lastname@example.org
Email sent by the world to the company (with the old provider set as the MX) will hit the old provider and then be forwarded onto Office365. The setting we changed above will allow O365 to deliver outside of O365 for users who don’t already exist. (it, both can now talk to each other).