There is no single best way - that said I prefer to keep in mind that businesses owners get inundated with offers.
100's of emails every day and week - so what are you going to do different..?
Instead of cold emailing - just like everyone else - why not set up a webinar and speak to people en mass.

This will leverage your time and your potential reach from 1-to-1 to 1-to-many.

Instead of humping for business - like everyone else - what will you do different to get their attention..?
could you walk in to local brokers?
Perhaps send something through the post
Build a relationship first..?

At this point - why would anyone open their client books to you?

You may well be surprised that money is not the only motivation - Doing business with people I like is a big motivation for me.

action steps - change the way you do business
get people on a webinar
promote your message to a mass audience
let them apply to work with you
Most of all - build relationships

Hope that helps
Regards
Phil

ps - call me if you need help with setting a webinar strategy like this up

Never cold email.

Cold call and introduce yourself, give a 30k feet view summary of what your background is. state that you want to meet in person to go over a product you are offering and ask for best availability. you will either get no, a date or questions.

all of which are really good for validation.

Your request specified email marketing, so I will leave the answer on that to the others.
That said I think for brokers you need to widen your approach. As a whole most buy into a product/service based on either a referral from a happy colleague, a recommendation from their circle, or a feature in a related industry article.

Cold email gets deleted almost without question and most brokers attention spans mirror my five year olds anyway. The webinar and cold email still should be a cheap and easy part of your marketing, but if you want to gain an audience you need happy early adopters and you are going to get those users differently.

Happy to have a call to discuss more. I've been in real estate 13 years and sold over 3000 units, as well as an investor in REtech companies.

I am a real estate broker and my first suggestion is lose the word "Pitch". How about using the word present as an alternative. That is from Tom Hopkins book by the way.

As a broker, I get so many "pitches" in my email account that most people have no clue that the email I advertise is really my junk email. So that being said it doesn't reach me. I delete them all.

A straight up phone call would be better than a sneaky email and your conversion rates will be much higher. Consider this. If you send emails out you will be lucky to get a 3% return call or response. I'd say it will be on the lines of 1% unless you have something that is so good it catches on real quick.

Your product must be able to solve a problem and save a ton of time in this industry or it's going to be overlooked.

Here are some brief things that get my attention IF I see an an email or if someone calls me.

1) Say on sentence that tells me if I am interested in what you have.

2) If that one sentence doesn't get a response like I am interested then GET OFF THE PHONE.

3) Send a thank you note for taking the call and give a little info on the what I call "call me cards". It's a postcard and not a letter you have to open. You can make cheap ones on your computer with stock online or get them at an office supply. Other options would be to order bulk online.

4) Consider you website and is it informative.

5) Make a video. Videos get more responses than typical websites because you don't have to read you listen.

6) I'd be careful emailing people just because of the spam laws. If they click through your provider that you are spamming you could easily get on spam list which would not be good for your company image.

7) Trade shows are awesome, but expensive. Figure 5k minimum.

8) Sponsor a free real estate seminar and have guest speakers. Then at that end tell about your product. You will have a captive audience.

9) Develop a brandable domain and a searchable domain. You can call me for more info on this.

10) Advertise in Realtor magazines.

11) Have a website where they can join as an affiliate. Once they join and place their code on your website they are paid referral fees through the link.

12) Automation online will be the key to your success in my opinion.

13) Use Linkedin.com today. Friend Realtors and then post things randomly so they see your post. Don't email them though.

Hope some of these ideas work for you.