Salesforce email relay to Office 365

I am hoping to get this setup without having to setup an internal IIS SMTP server.  Does anyone know the procedure for getting this setup correctly?

Currently when sending email from salesforce it is sent on behalf of the user.  All users have Office 365 mailbox.  I have configured a connector in Office 365 which allows it to work when sending email to company users but when sending to external it fails.
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FOXActive Directory/Exchange EngineerCommented:
In your office 365 admin center you have to create CONTACTS for your external users with their email addresses.  Once done you will be able to send to those contacts.
MinotAuthor Commented:
Is there any other way besides creating contacts?  We are talking potentially thousands of contacts.  Thanks
FOXActive Directory/Exchange EngineerCommented:
Did you test with one external email set up as a contact in O365 to verify if that worked? You can do a bulk import of the contacts into o365 with powershell and a .csv file.
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FOXActive Directory/Exchange EngineerCommented:
MinotAuthor Commented:
Not sure what fixed this.  I had originally followed these instructions and it did not work for external users.  I went back a few weeks later and re-enabled relay without changing anything else and it worked.  So the below link may be correct.  Thanks for the help.

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MinotAuthor Commented:
The link provided was the answer.
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