Outlook supports upper-case Margins, does that also mean every other email clients support upper-case 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.