One Time Use Contact List

What is your process for when you receive a list of contacts that you can ONLY use for a UNIQUE/SPECIFIC purpose and then are instructed to not contact them further? For example, we hosted an event, and received a contact list from someone who asked us to only communicate with that list of constituents for that event, and then to not add them to our general marketing or development communications. If you have experienced this at your organization, I want to hear from you.

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