email prospecting for local business, plain text or html?

I wonder what is the best way to format your email for prospecting?
I am sending some emails to the local business for SEO service. I wonder should I just keep it plain text or have some html formatting and look more interesting? But I suspect any html email automatically looks like junk mail as most business correspondent use plain text.
What is your thought about it and anyone with experience please comment. Thanks

Why don't you test both out, and use tracking to see which one has a higher open rate / CTR? I am sure everyone has a different opinion on this.

always text never use html

i am thinking some simple html for formatting, no pictures. Anyone can recommend good email software for tracking? or outlook is good enough to do the job?

Does the html email trigger any spam filter?