Syncing Direct Mail and e-Marketing Strategy

As we plan for our upcoming season we are looking at targeting groups of our mailing lists with e-communications around the same time direct mail pieces arrive in-home.  We're curious to know what has worked best for others: having an email hit the same audience a few days in advance or having the email hit after the mail piece is in-home?  Has this helped the overall direct mail performance?  How much time have you found works best between each communication?  

Thanks in advance for the feedback!

Best,

Chuck Buchanan

92nd Street Y