Hi WILLIE LUMP LUMP,
If you are using the Msn software to send and receive emails please follow the below given instructions to change your font size.
1. Sign in to your Msn account
2. Click on Help and Settings
3. Click on Settings
4. Click on Email settings Click on Writing e-mail
5. Click on font
6. Select the font of your choice and size of font
7. Click OK.
Please revert back for further assistance.
Thanks!