I was doing some research on how to make emails compatible for mobile devices, and found that recommended width for email is 600px and on mobile it’s 400px.
My question is that if i create two different versions of email template with different widths, is there a way to make sure correct template is displayed on Computer and Mobile?
I hope i am able to elaborate my question properly.
As others (as well as myself) have stated in other threads, I’ll simply say this:
The best width for mobile devices is 100%, fixed widths on mobile devices is like providing one size fits all clothing (which obviously unless it’s got an elasticated waist won’t do at all). Mobile devices range from the iPad (which has a large viewport region) to the really tiny cellphones which have pixel widths the size of the region to the left of this post which holds the username and avatars of the poster. Don’t use pixel widths for anything intended for mobile devices, just allow it to take up the full screen and use percentage widths (if columns are required for larger handheld devices) to ensure it scales correctly. 
I think your question is clear, but there may not be an answer yet (current generation of mobiles).
While we can try a little with web pages because of CSS and @media queries, HTML emails often need inline css… heck even table-based layouts work better due to such terrible CSS support for email.
I would think about sending non-HTML emails with the option to click to HTML emails… or the other way around. Some mobiles (like the web-ready ones that can zoom etc) can deal ok with larger sizes, while others can’t. So possibly giving an obvious choice to everyone might be best?