To get the right answer to the above question, don't ask former Donald Trump advisor, and attorney at law Sam Nunberg. Mr. Nunberg made the rounds of the cable news programs yesterday, and expressed his astonishment that he was expected to review and produce his personal emails in response to a grand jury subpoena issued in connection with Russia investigation of Robert Mueller. He wondered if it would take him 20 hours to review his emails - or then again he thought it might take him 40 hours . . . and even later he speculated that it would take him 80 hours! Maybe he should simply give the FBI the password to his email account!
An excerpt from the subpoena is posted here. It specifies that "Production with respect to each document shall include all electronic versions and data files from email applications, as well as from word processing, spreadsheet, database, or other electronic data repositories applicable to any attachments, and shall be provided to the grand jury where possible in its native file format and shall include all original metadata for each electronic documents or data file." The documentation relates to communications between Mr. Nunberg and Donald J. Trump; Paul Manafort; Steven Bannnon; Carter Page, and others, from November 2015 to the present.
Courts rarely find such requests for productions from personal email accounts to be burdensome. In Sunderland v. Suffolk County, 2:13-cv-04838-JFB-AKT (E.D.N.Y. June 24, 2016), Magistrate Judge A. Kathleen Tomlinson ruled that, "the Court concludes that Plaintiff has the right to pursue emails and other correspondence the Individual . . .. Defendants may have created/saved on their personal computers or sent from their personal email accounts. The Court does not consider the requested discovery unduly intrusive or burdensome. " The defendants in the suit were physicians. A transgender inmate brought a 42 U.S.C. 1983 action against them for violations of her rights under the Eighth Amendment. The document request was limited to a date range of four years, and the parties agreed upon particular search terms. The limited excerpt of the subpoena doesn't indicate if search terms were proposed to Mr. Nunberg, but if they were not, proposing such terms might appear to be the logical next step for him to take.