change default font when reading message

[SteveS]

I am using Outlook 2003, use word for editor and reading of rich text and I
compose in HTML

When I read messages i want to change the default font to a larger size.

I have done tool>option>mailformat>startionary and fonts but
emails from outside my network come thorugh with changes and emails from
inside the network do not.

Any suggestions other than select all and then
tool>option>mailformat>startionary and fonts

Thanks
Steve