how do I increase the font size in my email and maintain resolution.

Two things you can do to easily aid with readability in Mail are as follows:

1) Increase the size of folders in the sidebar:

a) select "system preferences" from the Apple menu

b) select "general settings"

c) select small, medium or large under "sidebar icon size"

2) Increase the text in the main body of the email (both sent and received):

a) select "preferences" from the Mail menu

b) select "fonts and colors"

c) adjust font size for "message list font" and "message font". I have noticed this works properly while in classic mode, but in regular mode the message list font doesn't appear to change size.

Select classic mode by accessing Mail preferences and selecting the "viewing" tab.

Another shortcut is to right click on the toolbar, then select "customize toolbar", and then drag the "smaller / bigger" buttons onto the toolbar. Now you can decrease and increase font size as desired on the fly.

If you don't want to decrease the resolution (which would increase everything), then you will need to go to Preferences of every application to increase the font sizes. In Mail, go to Preferences > Fonts & Colors:

Documents: depends on the application you're using - but check Preferences and check each area/option. Same in Finder > View > Show View Options.