Have you got a list of leads, potential customers, or existing database of people and want to identify or target those that are using Office 365? I can think of one or two scenarios where this would be handy!
Microsoft have a free modern Excel Add-in called “MX Lookup” (available in the Office Store) that takes a list of email addresses and will perform a lookup for each email address and will tell you if the backend mail system is Office 365 or not. Pretty handy right?
I’ve been using this add-in in demos and have recently noticed that it now identifies Outlook.com accounts as being Office 365 (where it originally identified these separately) so be aware that you may get a mix of Office 365 and Outlook.com users.
Cameron Dwyer 
Maybe since your post they have “fixed” it 😀
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I tested this again today and @Outlook.com accounts get identified as “Office 365” accounts. I don’t necessarily think that this is a bug (or problem), I think it’s more a case that Microsoft is slowly transitioning to merging the backend services between the personal (consumer) world and the business (work & education) world. We are seeing this both in the backend services and also with some of the client applications getting merged together which I think we will see more of as Microsoft executes on this strategy.
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