Say you have a website with email links and you want all of the ‘mailto:’ links to create the message in Office 365 (instead of Outlook desktop app).  Well you can. Simply build your email link like so:

https://outlook.office.com/owa/?path=/mail/action/compose&to=[email address]&subject=[email subject]&body=[email body]

Here is how you can email me through Office 365 click here

In the most basic form you could simply leave off the subjects and body and only include the email address like so:

https://outlook.office.com/owa/?path=/mail/action/compose&to=[email address]