Set your email client to compose in plain text

Outlook:
Create a new email message. Go to the Format menu. Select Plain Text.

Outlook Express:
Create a new email message. Go to the Format menu. Select Plain Text.

Eudora:
With Eudora open, go to the Tools menu, choose Options.
For Category, scroll down and choose Styled Text.
Select the "Send plain text only" button.
Hit OK at the bottom.
Then compose the all-campus and send it.

OSX Mac Mail:
Create a new email message. Go to the Format menu. Select Make Plain Text.

Thunderbird:
Create a new email message. Go to the Options menu, select Format, select Plain Text Only.

Webmail (Mirapoint):
Create a new email message. Click the plain text option in the upper right corner.