It is possible that the person who sent you the original email used eg: MSWord to compose the email or they inserted css code to control how their email would look. In which case they chose to send the email with a load of css coding and this maybe controlling the font.

Locate original email, so you can read contents in Message Pane. click on the 'More' button and select 'View source' Scroll down to the 'Content-Type: text/html; ' section.

Do you see something that mentions -microsoft-com:office:office or similar.

below this would be a load of css info for font, borders, tables etc. Do you see a section with anything like that?

I've got an email from British Gas and if use 'Reply' or 'forward', it controls the font colour. but after writing the email, I can highlight all my text and then use the Formatting Bar to select a different colour for the font.

RE: and cannot be changed to another font. Is the 'Formatting Bar' enabled ?

Thanks for the quick reply.

Yes, the 'Formatting Bar' is enabled and all attributes can be changed EXCEPT the font. Color, size, bold, italic, underline, justification, even bulleted or numbered lists work fine.

This occurs when forwarding some HTML messages. For example, try forwarding a YouTube notification. When forwarding, the font in the 'Formatting Bar' shows "arial,Arial,Sans-serif" rather than the default font. This only occurs when forwarding inline, rather than as an attachment. I imagine your British Gas email would act in a similar fashion.

Shouldn't the original post's formatting be encapsulated such that it does not interfere with the new text response? Is it because the editor cannot handle multiple \<html\>\</html\> sections in a single message?