A mail ballot grace period allows election officials to accept and count mail ballots that arrive after Election Day, as long as the ballot was postmarked by Election Day. Grace periods vary by state: Mississippi allows 5 business days, while other states allow 3, 7, or 10 days. Grace periods exist because the postal system cannot guarantee next-day delivery, and postmark dates verify that the voter acted by the legal deadline. Fourteen states and D.C. have grace periods for all mail voters. About 29 states have grace periods specifically for military and overseas voters under UOCAVA. Watson v. RNC puts all of these grace periods at legal risk.