Using Dynamic Lookups in the client interface
When using Dynamic Lookups in forms used by clients (end users), there can be privacy considerations.
An Autocomplete brings back a list of all items in the lookup file. There are usually no privacy considerations if the information being brought back is Matter numbers, Project names, or the like, but if the information is personal contact information, it is generally not appropriate to be using an autocomplete in a form used by clients as the list will give clients information about other clients.
For Client contact information in client interface forms, set up the email address, or staff number, or other key you are using for bringing in client contact information, as a Dynamic population only:

This will provide a field where the client enters their key piece of information, such as their email address in the example form below, and the Dynamic population will automatically fill all the other fields.

If you are concerned about clients seeing this automatically inserted information, you don’t need them to check it and change it if necessary, and you are not expecting users who are not in your lookup file to use the form, you can hide some or all of the fields being populated by the lookup so that the client cannot see that this data is being automatically inserted (Set the fields to Hidden in the Request forms design).
Library staff are considered to be trusted employees and so the considerations described here for client forms, do not apply to use of Dynamic Lookups in the staff interface.