Email marketing can be a really powerful mid-funnel tool for companies who do it right. However, if you want to screw it up royally, there are four principles you will want to keep in mind:
1) Send emails so long they need a table of contents
If your email can fit on a screen, you're not going to exhaust your audience the way you want. Maximize the annoyance by adding every conceivable piece of content into one eternal email.
2) Always focus on what you want to say
It doesn't matter if you send emails daily, weekly, or monthly; make sure that every time you send out an email, it is all about what you want to tell your audience. The key is to make sure that every communication is asking them to buy, schedule, sign up, donate, or share something that benefits you.
3) Treat every email subscriber the same.
Make sure your newest lead and your best customer are on the same list receiving the same content. You want to avoid segmentation, context, or anything else that might help to nurture the relationship between you and your audience. Keep it cookie cutter, and keep it all about you!
4) Add every email within reach to your list.
Connecting with random people on Linkedin. Setting up a fishbowl drawing for an iPad. Wrapping your hands with duct tape and serpentining through an exhibition hall. All of these are great ways of growing your email list with people who will learn to hate your company. Unfortunately, it's illegal to not include an Unsubscribe button at the bottom of your emails; just make sure you add more than you lose.
However, if you want your audience to enjoy hearing from you, do the opposite of everything I just said.