blogs.msdn.microsoft.com/carloshm/2016/01/16/how-to-compose-a-new-message-or-event-and-populate-fields-in-office365/
https://outlook.office.com/mail/deeplink/compose
- subject
- body
- to
https://outlook.office.com/calendar/deeplink/compose
- subject
- body
- location
- startdt 2016-02-29T19:00:00
- enddt 2016-03-01T00:00:05
https://outlook.office.com/mail/someone@example.com/inbox
Remember that for more complex scenarios, you have available Outlook API, mail, calendar and more
https://teams.microsoft.com/l/chat/0/0?users=someone@example.com
SO on gmail urls https://stackoverflow.com/questions/6548570/url-to-compose-a-message-in-gmail-with-full-gmail-interface-and-specified-to-b