When you are engaged in email marketing it is very important to know and monitor the result of the work done. To do this you must use a range of efficiency indicators.
The first indicator is Number of Subscriptions. It shows how many active customers are interested in your product or service. To increase the number of subscription you must provide the users with something valuable and interesting for them, such as articles, tips, e-books, free video tutorials and so on.
The second is Open Rate Index. This index demonstrates the number of your letters which were opened and how many subscribers found out about useful information or an advantageous offer. To increase this index you need to make the title more attractive.
The third is Click Rate. It displays the number of users who have performed an action (click) in the letter and went to the site, or download the product. Work on the design and filling of the letter to make this rate higher.
The fourth is indicator of users who have Unsubscribed from the mailing. The total percentage of unsubscribers should be within 1-2%. If it is higher you should change something in your email marketing activity.
And the most important is Conversion rate of purchase on site. This indicator is the result of the work that you have done. If the free email marketing campaign was correctly planned, the indicator will be high.
So, now you know how to assess the level of your email marketing and what it depends on. Good luck !