SIP address overwritten (breaking Skype Business) when alias added via Dashboard
Summary: SIP address overwritten (breaking Skype Business) in Office 365 when email alias added via Dashboard.
The problem is explained in perfect detail at the link below. It does still happen with current Essentials 2016, and it happened in the previous version, too (2012R2).
All you need to do is use the Essentials Dashboard to add an email alias to a user in an Office 365 tenant that also has Skype for Business. Then edit that user's mailbox in EAC and look at the Email Addresses section. The new SMTP alias will be there, but the SIP entry that had been there is gone.
It's probably time this is fixed.