From my former employee and my current experience with email lists:
- Avoid purchased lists at all costs
- Apply double opt-in to confirm someone really wants to hear from you (most of the email software supports this out of the box)
- maintain a healthy list (no duplicates, dead domains etc)
- do not let your list to be covered by dust (for example: if you collected an email and consent from someone a year ago, and there were no sends to this person since, consider removing it from the list).
- Spread sends in time - bigger email providers have special requirements for mass mailing, and you will have your sending domain reputation busted if you would not comply.
Additionally, treat the "opens and clicks" statistics with a grain of salt as they are basically unreliable these days - Apple Mail will read that email before the recipient does, Microsoft outlook will click all the links on the message to check for malicious content, some email clients will not fetch images from the message (hence no image responsible for click would be recorded).
