An Html message composer should try, where possible, to not hard code font sizes or fontnames. As they have no way of knowing what default sizes and names are set up by the receiver. Also if hard coded, there is no flexibility in changing the font information. For instance most browsers allow for a user to increase or decrease font size on the fly with a keystroke or mouse button.

IMHO  do not know of anyone who writes messages using CSS, and it is also unlikely anyone, except for web server admins to be writing text in Html markup tags or CSS markup. 

Martin 

1)  I would like to know if Pegasus mostly uses the modern CSS way of setting styles such as font size whenever possible.

I ask this because I was astonished to find that Thunderbird still uses the HTML method of setting relative font sizes.

I thought this was deprecated a long, long time ago now!

It causes problems with, for example, the Fastmail web client, which doesn't recognise these font sizes, which is correct if it is to be in conformity with the modern standards. 

2)  Can Pegasus Mail successfully read and compose using unusual O/T and T/T fonts?

For example, a closed group of correspondents may agree among themselves to use all the fonts in emails that come with Windows Vista.