Email marketing Giant Mailchimp gathered anonymous statistics so you can compare your effectiveness of your campaign to others.
It even segmented info different industry for a more actuate comparison.
A few highlights:
Open rates: 21.09%
Click rate: 2.61%
If the email list is built correctly, email marketing is still one of the most effective channel for marketing. 2.61% average click rate, and 4.78% in "Hobbies" section.. It's just impressive.