Tips for Collecting Email Addresses
Some email collection methods can increase the amount of invalid email addresses and/or Spam Complaints. When collecting email addresses, make sure the person giving you their email address knows exactly what you'll be sending them. This way they won't report your mail as spam, or enter an invalid email address.
You can also add a link to your website for visitors to opt in to your email campaigns. For more information on creating an opt-in link for your website, see Adding Express Email Marketing Subscription Links to Your Website.