We have been using Windsor Circle's services for the last few years and they are experts at retention automation!
We have been able to send automated emails that we would not be able to do without Windsor Circle. Things as simple as wishing our customers a happy birthday and things as complicated as notifying our customers that they have qualified for a loyalty reward have all been able to be accomplished with minimal effort on our part.
I cannot recommend Windsor Circle highly enough! - quoted from review on MagentoConnect.com