Source for Microsoft Outlook supporting Margins.

Gmail, Yahoo! Mail seem to support margins with an uppercase M. I did my own tests and can verify that they both work.

However, I'm not sure if all other email clients accept margins with an uppercase M? I don't have a lot of emails to preview, particularly for Android devices.

And this can be extended forward to cases where there may be uppercase P for Padding, uppercase letters for certain CSS properties, and such that Outlook may support.