Email is fine, easy and (almost) free, but nothing beats the deliverability of the good old post office! Send out custom postcards to stand out from the crowd. Again, use tracking to determine how your postcard campaigns are converting by setting up a special URL, e.g. www.yoursite.com/postcard. This way you can split test different card designs, headlines, call to action, etc. to see which one pulls better.
For large-scale mailings (5,000 or more cards) use a commercial printer and mail shop to deliver your cards. If your list of prospects is smaller, and you’d like to deliver personalized postcards, greeting cards you could use SendOutCards. It’s an online on-demand postcard printing and delivery system that works very much like sending personalized email, only it prints, personalizes and mails real postcards and greeting cards in any quantity. You can send a dozen custom postcards for about 10 bucks. I use this service myself and I love it.