Configuring Outlook to always reply in plain text

For Googlers, since I had terrible trouble finding this. Information originally from here.

How to set Outlook to always reply in plain text, regardless of the original email format:

In Outlook, click Tools -> Options
In the Preferences panel, click “E-mail Options”
Tick the boxes for “Read all standard mail in plain text” and “Read all digitally signed mail in plain text”
Click OK

The above instructions work for Outlook 2003 – the link has instructions for other versions. It requires that emails are always read in plain text, but it’s the only method I can find that doesn’t macros, weird HTML stripping programs or reconfiguration for every email.

I looked at that options panel at last twice while trying to figure it out, not sure how I missed it!