You may not know it, but every time you send an e-mail from your computer, you are also revealing the location of your PC; as the IP address forms part of the header of the e-mail.  To avoid this, many security-conscious users use webmail instead, which generally does not include this feature.  In fact, in 2013 Microsoft explicitly removed the IP address from Hotmail, to improve the privacy of end-users.

The feature is also not supported in Gmail, Yahoo, AOL and Outlook.com.  What potential corporate whistleblowers might not know, however; is that Office 365, unlike Outlook.com, does by default include your IP address, and shares it to anyone you send an e-mail to.

The feature was included on purpose by Microsoft, to allow enterprise administrators to search for e-mails by IP address. Reportedly, this is useful in finding the location of a sender in the event that the account has been hacked.

Office admins do have the ability to disable this feature by creating a new rule in the Exchange admin centre that removes the header.  For everyone else, you should probably know that if you plan to pretend to be working from home, sending e-mails using the web client is not going to fool anyone.

Source: bleepingcomputer