Legit Casting Companies to Email?

Hey everyone! So I’m finally taking a step forward and made an acting profile on Backstage (no membership, I’m too broke for that). I’m now in need of how I should take the next step.

In my opinion it, makes the most sense to start emailing casting companies and casting directors. If anyone has any advice on how to properly do it, that would be much appreciated. The main thing I need is what casting companies/directors I should email. Again, I would appreciate any help!