First things first. Sending a cold email to a prospect before calling them doesn't "warm" them up.
The definition of a warm lead is when a prospect is raising their hand. That's it.
How many times have you sent an email out, tracked it with tools that told you when the prospect opened the email only to call them and have them still give you some sort of blow-off or stall? I'm betting a lot!
How to really warm up a lead via email marketing
Understand that the end game is to get your prospects to reach out to you! A warm lead is when a prospect raises their hand (by either picking up the phone and calling you or filling out a form on your website and submits a request to be contacted).
If you truly want to "warm up" leads for email marketing, here's what you need to do:
1. Start with a quality list
This means use resources that attract your target audience that want to hear from you again. Developing and then promoting valuable "how to solve" webinars is a great way to attract targeted prospects and build your email marketing list. You will want to stay away from purchasing lists, etc.
2. Be consistent
Sporadic "Hey, we need deals so let's blast out a mass email" campaigns often do more harm than good. You want to have well-thought-out material that goes out on a consistent basis for your audience to read.