We use to send out a company news letter monthly, (worked great) but got really expensive with thousand of clients, switched to E-mails and response tanked! To easy to delete and people hate business E-mail IMO. We also were only able to collect maybe 20% of our clients E-mails as we started doing it so obviously that hurt as well. We still collect them to send thank you's, but that's it.
We now are using a text reminder program and I bet this is going to be golden! our clients are very open to it and we explain how it works to them at the end of ech job.