display font size too small

I am new in this forum.
I’m using em-client version 7.2.35700.0 on a MAC with Catalina 10.15.3
My question is concerning the displayed font size of new/forwarded messages.
So it is not about real font size of the msg.
I receive your mail and it it is displayed very well readable. (see example 1)
I hit the “forward” button and it is displayes in a very small display font, which is hardly readable. (see example 2)
My question: how can I adjust the displayed font size to be larger, so that it is readable?
I do not want to adjust the real font size of the msg, since this is annoying for recipients.
Any Idea?

Example 1

Example 2