Email Marketing, Yes or no?

What's Email Marketing? Should my business make use of it? What is it about? Pros and Cons? Here's a short article about this service.
What’s Email Marketing?
Email marketing is the direct equivalent of direct marketing, but online. Meaning, given one message, you need a database with the target audience’s email addresses to send the message.
What are its Pros?
1) Its low cost compared to any other means of direct communication.
2) It’s a highly trackable medium, and allows us to track retention, how many times the message was opened, and what parts of it caught the most interest from our clients and target audience.
3) It’s the best way to reach some demographic groups.
What are its Cons?
1) For some population segments, Internet presence is low.
2) Used in a non-professional manner, message presentation might not be the same in all email platforms and systems.
3) Used in a non-professional manner, the message might be perceived as spam.
Advice
1) Create a text version and an html version, and provide the option of choosing which one to receive.
2) Always include a link to an html version hosted in your website.
3) Include links to unsubscribe.
4) The message can’t be more than 30-40 Kb.
5) If it includes third-party ads, they need to be a clearly separate part of the message.