Five Tips to Better E-mail Campaigns

2) Twenty percent to 40 percent of e-mails aren't delivered. Understand how to read the report that your e-mail system gives you on delivery, and understand that the numbers you get on delivery do not include e-mails that were swallowed by filters.

"So you have to know that there's a bigger problem with delivery than you think and there's a variety of things you can do about that ... one thing to look at is ... any people on your list who have not opened or responded to an e-mail in a long time. Maybe you're being filtered there," Holland adds.