Is there a way to create a new alias to a email address in office 365 from a .net application / web page? I've looked for a API, but couldn't find any.
Ok, so I found out that you can use PowerShell to add aliases to a email address. And PowerShell can be used with c# to connect to Office 365.
Connect to Office 365 with .NET with PowerShell
http://gsexdev.blogspot.se/2011/07/running-exchange-online-and-office-365.html
Add alias to a email adress with PowerShell
http://wdmsb.wordpress.com/2013/02/04/powershell-for-office-365/