The compilation finds that capturing e-mail addresses when consumers are highly engaged was found to be the quickest and most productive way to grow the files. Those points of contact include point of sale, consumers shopping online, and in-store via text messaging. These methods rated as much as 60% higher over such offline tactics, including mass advertising and list rentals.

Morgan Stewart, ExactTarget's director of research and strategy, quoted in a release said "... list growth tactics are built on gathering subscriber data rather than hunting for it... the best way to grow your subscriber list is to collect information during customer-initiated interactions."

On the other hand, the most inefficient ways to try to capture the addresses, according the study findings, include through outbound call centers, list rental, e-mail append and offline advertising. In addition, the report notes that one worrisome finding is that 33% of all e-mail marketers don't bother to evaluate the performance of their list gathering techniques.

Other top findings reported in the whitepaper include:

• The best performer for capturing e-mail addresses: Onsite registration followed by inbound call centers, point-of-sale and through social sharing
• B-to-B marketers showed better results capturing the address with incentivized registration, while B-to-C marketers find non-incentivized subscriptions most effective
• Mobile phones are the up-and-comer when it comes to capturing, or allowing customers to subscribe to e-mails. This method is expected to increase faster this year than any other list growth tactic... more than 500%
• Enabling subscribers to share e-mail content with their social networks is expected to increase more than 348% in 2009

Tamara Gielen, founder of The Email Marketers Club, concludes that "There is... no one tactic that will provide meaningful list growth... successful list growth strategies employ... tactics to drive new subscriptions and compel subscribers to register because of the value of the communication itself."

The complete 2009 List Growth Whitepaper is free and available for download online here.