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.