Microsoft's acquisition of Skype led to the eventual death of the standalone Skype account. Microsoft wouldn't continue to grow a standalone authentication directory when it already had the Microsoft account infrastructure in place.
For existing Skype users, it offered to "upgrade" your Skype name to a Microsoft account by simply adding your email address. Now, new users of the consumer platform must create or use a Microsoft account.
If your small business started out using Skype, or your users are comfortable with personal Skype accounts at home, everyone's in for a shock.
Microsoft doesn't split out monthly active users by product, so we're left with a large Office 365 lump.
The current 85 million MAUs include kiosk workers who might only use a mailbox.
You can chat with them and see their presence indicator.
Access your Skype for Business contacts via Office 365 in your browser (finding the Skype icon above Mail or People) and the directory search will find new contacts by their Microsoft account address, but never by their Skype name.
Same limitation with the Skype for Business for Mac client, which has no luck finding old Skype names.