Anita,
Getting email from my members and the font and font sizes are coming
very small. Is there a way to set a default here?
No.
If the messages are sent as plain text then the font size is controlled by your email viewer.
If the messages are sent with formatting (HTML) then the font size is controlled by the sender. Unless you use the group setting for "Plain Text Only" - that will strip the sender's formatting.
In either case, if you are looking at the messages through a web browser you likely can use its "zoom" tool to change the size of all text on the page. The controls for this vary by browser, but I think most use Ctrl plus the keypad + - and 0 keys as shortcuts.
Shal