Word-of-mouth leads in Denver (update)

Two small Denver employers told me they are hiring but have not posted yet. I do not usually post, so bear with me. They like a brief email with a résumé. What do you write in a cold email?

A short email with two sentences about what you can do and your résumé attached worked for me. I followed up after a week.

Visiting in person worked for a trades job. For office jobs, email was better.