Are envelopes generally involved? In the Antrim County dispute[1] it sounds like they use Image Cast Precinct (ICP) tabulators[2][3]. This[4] appears to be a video of one in use[5], and it doesn't seem to involve an envelope. If there's 100% mail-in voting then yes every ballot would have an envelope. But if there's any less than 100% then there will be less envelopes than ballots, so I'm not sure envelopes would be too useful for recounts.