1. This is Personal
A handwritten, innocent looking envelop has the most chances of getting opened. Do you want to raise funds for an organization, you have an offer? Try a nondescript look for staggering results.
2. This is Time-Sensitive
Try including a quick short message that lets the receiver know that whatever is inside will expire soon. This technique usually gets people to tear an envelope open.
3. This is Mysterious
If you want to include a teaser on the envelop, be sure to keep it very vague. Giving away too much information will have the opposite effect.
4. This is Important
Adding a seal that claims this envelope confidential, exclusive, priority or important makes receivers feel that this envelope is more important than anything else in their mailbox.
5. This is Simple
Some people avoid opening an envelope because they assume that it will ask too much of them. Maybe the offer is too complicated, maybe the action you will require them to take too tedious. Include a quick statement on the outside that lets them know that this will be quick and easy. Something like; will only take 2 minutes of your time, 3 easy steps and done, etc.