Stop mail changing font from pastes

Every time I paste something into an email in the mac mail client it screws up my font and changes it to whatever the font of the painted text is.

What's even more annoying is I can't change it back so I have to type stuff into manually unless I want my email to look bizarre.

How do I stop this?!

Use the Edit Menu's "Paste and Match Style" option when pasting from other apps.

Setting Plain Text as your default email style will do the same.