Small employers hiring around Sacramento, social media manager here

Two small Sacramento employers told me they are hiring but have not posted yet. I have been trying to stay organised about it. 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.

Keep everything in writing and save the confirmation numbers. It saved me later.