The way that your users are sending emails doesn't really give you the ability to control who they email the record to. What you may want to think about is putting some process in place where the user has to create a Child record and select a User from a User field that is set to only include those users you allow emails to be sent to. Or possibly, if your process is simple enough, you could always have a User field - maybe an "Assigned To" field directly on the record. Your users could edit that record, select a User, and then on Saving, you could have an Email Notification set to automatically send to the user selected in that field.
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Blake Harrison
bharrison@datablender.io
DataBlender - Quick Base Solution Provider
Atlanta GA
404.800.1702 /
http://datablender.io/------------------------------