S.C. Code Ann. § 7-15-700: Delivery of valid military-overseas ballot; declaration of voter.

(A) A valid military-overseas ballot must be counted if it is delivered to the address that the State Election Commission or county board of voter registration and elections, as appropriate, has specified by the close of business on the business day before the county canvass.

(B) If, at the time of completing a military-overseas ballot and balloting materials, the voter has declared under penalty of perjury that the ballot was timely submitted, the ballot may not be rejected on the basis that it has a late postmark, an unreadable postmark, or no postmark as long as the ballot was received in accordance with subsection (A).