I would like to send a mass mail out promotion for commercial cleaning company, office buildings, doctor, dentist offices etc. not sure what is the most effective way to do this.

Are you talking about an email blast or a direct mail campaign?

You can get local business mailing addresses from a phone book, and I would suggest doing that with a direct mail campaign.

If you do an email blast, that can get tricky because of the CANSPAM regulations. A person or business needs to opt-in to a mailing list before you are allowed to send them blast email marketing.

Thank you for your quick response, yes looking for direct mailing, needing help with the actual letter itself, the content, I want to make sure it is effective.
Thank you

Well why don't you offer special promotional discounts to new clients, and additional discounts to new clients who mention the letter? Do you want to be a personable "small" business, or have a corporate feel? Make sure you portray that in your letter.

Do you have a Mission Statement and Core Values? Those will help you introduce your company to the community and in any communication and business down the road so make sure you write those!

You want your prospective client to know that you're passionate about your work: and your work is ensuring that their environment is clean. That's an important job! Good luck with your new business.