Even assuming the emails were lost before a litigation hold could be placed (or despite a litigation hold being in place), at the very minimum, it seems "good faith" means that the IRS should have notified Congress in February that it lost the emails. Rule 26 would have required Congress to do so. Indeed, such notice would have brought this issue to the forefront and could have saved a lot of money - the money it apparently has already cost to piece together some of the emails, and the money it will cost as the parties argue over whether the IRS negligently or willfully destroyed evidence. If the IRS had been upfront from the beginning, then subpoenas could have been issued months ago to other agencies who, as employers of the lost email recipients, might have copies of the missing emails.
If this discovery issue had arisen in federal court, the IRS would have likely been subject to monetary sanctions and possibly an adverse inference instruction. Shouldn't the IRS be held to these standards?