Texas Rules of Civil Procedure

Rule 196.4 Electronic or Magnetic Data.

To obtain discovery of data or information that exists in electronic or magnetic form, the requesting party must specifically request production of electronic or magnetic data and specify the form in which the requesting party wants it produced. The responding party must produce the electronic or magnetic data that is responsive to the request and is reasonably available to the responding party in its ordinary course of business. If the responding party cannot - through reasonable efforts - retrieve the data or information requested or produce it in the form requested, the responding party must state an objection complying with these rules. If the court orders the responding party to comply with the request, the court must also order that the requesting party pay the reasonable expenses of any extraordinary steps required to retrieve and produce the information.

Rule 193.3 Asserting a Privilege. (excerpt)

[...]

(d) Privilege Not Waived by Production. A party who produces material or information without intending to waive a claim of privilege does not waive that claim under these rules or the Rules of Evidence if--within ten days or a shorter time ordered by the court, after the producing party actually discovers that such production was made--the producing party amends the response, identifying the material or information produced and stating the privilege asserted. If the producing party thus amends the response to assert a privilege, the requesting party must promptly return the specified material or information and any copies pending any ruling by the court denying the privilege.