You may want to send this certified mail, return receipt requested.
1234, Main Street
Boston, MA 02123
06 April, 2005
<Recipient Address Goes Here>
According to the order of the court, your <child support/alimony> payment of <$insert amount> is due on the <date due> of every month. This means that your <payment/payments> for <names of months overdue> are overdue. Please submit payment in the past due amount within five days from the date of this letter to avoid further legal proceedings.
If there is some reason why you are unable to make the requested payment at this time, please advise me immediately so that we may work out an agreement to bring the payments current.
I look forward to hearing from you.
encl: <List of enclosed items goes here>