Any way to increase the display and default font SIZE?

Any way to increase the display and default font SIZE?

I'm just setting up my mail accounts and the size of the display font is tiny. It doesn't appear to be customizable, or am I missing something? I see where I can change the font style, the interface color scheme etc., but no way to enlarge the font? 

I'd also like to set the default font size for email creation. I can set it for the signature, but not the body so does this have to be done manually every time? 

Why are the zoho fonts so small? I was really excited to switch to zoho but this may prevent me from going through with it.