that seems like an awfully high number of returns. any idea why so many?
i typically get 4 or 5 out of every 50 i send out. one possible alternative is to print “'forwarding service requested” so the post office will notify you where the person now receives mail.
I would recommend that you find another source for the names and addresses. Almost half of your mailing came back undeliverable. That is a very high percentage. In my last mailing of 120 postcards, only 10 came back undeliverable. These were because the houses were vacant. As far as I am concerned, that is a great little piece of information. I can track down the owners of the vacant homes.
As for what to put on postcards, I put about the same stuff I put on letters. Just abbreviated somewhat and naturally in a smaller font.