No, it is not. He can use the account for personal email but that does not make the account itself personal. If you use an account provided by a third-party for

No, it is not. He can use the account for personal email but that does not make the account itself personal. If you use an account provided by a third-party for personal emails then you cannot expect that email to remain private. It is subject to whims of the third-party and applicable laws. Although in terms of FOIA, as I understand it, one can expect unrelated emails of the request to not be released. But if one writes a small sentence relating to the subject of the FOIA request in an otherwise personal email, then it is subject to that request.