I think zoom is the wrong way to go about it.

Go to Tools|Options|Display|Formatting, click on the Advanced button and set the font size. The "Minimum Font Size" setting is especially useful. Note that these sizes are in pixels and will need significantly larger numbers than you might use for points.

You probably need to set these for both "Latin" and "Other Writing Systems".

Thanks for the quick reply. I had already tried that. What I am looking for is a way to permanent set the zoom. Like with CTRL and the + key or the scroll wheel.

There is no way I know of to pre-set the zoom level.

How does setting the type size not meet your requirements?

Font size doesn't affect HTML messages.

It does here.

Did you set all the font sizes, and in both Latin and Other Writing Systems?

Toad-Hall has described a method somewhere using the userContent.css file to set a default size for message text. If I can find it we can see if it helps you.