Given I'm creating a mailto: hyperlink. Is there a absolute limit to how much data you can put in mailto: body parameter?
Is this browser dependent?
I believe these is a limit to the mailto URI. And I believe that limit is dependent on the browser.
Check out this question and answers: Getting around mailto / href / url character limit
Like they suggest in that answer, I would suggest doing some sort of server side processing of the data, most likely in a POST over a GET.
Also from that question, this link (http://support.microsoft.com/kb/q208427) was presented and tells that IE has a limit of 2083 characters in a URL.