First, include an eye-catching Send-to-a-Friend (STAF) graphic in every e-mail. It should be at the bottom of the e-mail, following the gist of the message. Recipients won't be motivated to STAF unless they know what you're offering, and they won't search to find this option.
Friends must be able to add a comment to the top of your e-mail. If the e-mail is merely a forward in the friend's name, the recipient may not notice and think you've spammed them. The friend's endorsement, e.g., "Check this out," is the most important line of copy in your e-mail. Similarly, the friend's name should be included in the subject line of the forwarded e-mail: "Jane Doe thought you'd be interested in this."
The forwarded version must have a link to your opt-in form. The goal, after all, is to get the new friend to become a permanent subscriber. You must also provide this option for people who don't use your forwarding functionality, but instead hit the "forward" button in their e-mail program. On your original, outgoing e-mail, include language such as, "If you received this e-mail as a forward, we invite you to subscribe."
Monitor your STAF Rate: # of STAFs/# of Responders. What percentage of your readers felt moved to forward your message? You won't capture all of them, for the reason described in the paragraph above, but you'll still capture a useful statistic. It is interesting to compare the STAF Rate with the Disaffection Index,which is, as I wrote in in a previous column: # of Unsubs/# of Responders. When your Disaffection Index is high and your STAF Rate is low, you know your message/offer was off base. When both rates are high, it's a good indicator that your message was not well-targeted: some loved it and some hated it. This stat, particularly when viewed as a trend and by consumer segment, gives depth to your response reporting.
Don't provide an incentive for forwarding e-mails, or you are likely to get bad addresses, angry recipients and run afoul of pending changes in CAN SPAM. It also makes the potential forwarder feel somewhat "dirty," like a cog in your marketing machine. But do thank Friends who forward. They are helping build your list with high-quality subscribers.