When federal courts are evaluating digital evidence from computer-generated records, what exception is applied to hearsay?'

Business-records exception

Explanation:

The Business-records exception which is also known as the Business Entry Rule, this is an exception to the evidentiary rule (which rules out hearsay from a trial) that permits business records to be admitted if the appropriate foundation is laid to show the document is dependable and can be relied upon.

The type of letter they are looking for is an Inquiry Letter. 
An Inquiry letter asks questions or elicits info from the recipient. They would include what they are looking for or what they need to know about. They should include any info to reach back to them.