If you use Netscape you can set the wrap length of your lines by going
Edit -> Preferences -> Mail & Newsgroups -> Messages
The side window has a line that allows you to set the line length of outgoing messages. "Wrap outgoing, plain text messages at __ characters." This reinforces the need to send plain text messages.
To make sure your Netscape browser is set to send messages in plain text go
Edit -> Preferences -> Mail & Newsgroups -> Formatting
In the side window choose "Use the plain text editor to compose messages".