How can I send plain text only emails.

How can I send plain text only emails.

Certain contacts have specified that they would prefer to receive my newsletter in plain text.

Is there a way to send plain text only emails?

I can see two options:

1. Send plain text & html - I don't want to do this as they will receive 2 messages, one which they can't read which does is likely to get marked as spam.

2. Send html only - Don't want to do this.

As there is a html only option is there not also a plain text only option?