I believe that communication is not achieved without a system of repetition. In the advertising business, the rule of thumb is that an advertisement must run three times in order to be effective. In speech-writing, we have the old adage "Tell 'em what what you're going to tell 'em, then tell 'em, then tell 'em what you told 'em."
This rule does not fail for direct mail, no matter how elaborate the package. In fact, if you're mailing an expensive package, the best approach may be to mail a heads-up piece, the big package, and then a reminder postcard, all carrying the same message.
MarketingSherpa: New Direct Postal Mail Results Indicate Re-Mailing Works Even Better in the Internet Age. 2007-Aug-20 (paid subscription required), by Anne Holland: Here's what startled me: in both cases, the results for Rab's second postal mailing were far closer than I expected to the response rates for the original wave....For example, one original wave got a 1.90% response rate with the follow-up achieving 1.46%.... Rab actually mentioned he had tested a campaign last year with both a multipage catalog-style self-mailer as well as a follow-up postcard. He got far less than 1% response rates from people who got either the postcard or the self-mailer. However the people who got both resulted in a 3.78% response rate.