For registered voters voting by mail, "date of mailing" means the date of the postal cancellation on the envelope in which the ballot is returned to the election official by whom it was issued. For all service and overseas voters, "date of mailing" means the date stated by the voter on the declaration.
RCW 29A.04.031
Date of mailing.
2011 c 10 s 4; 2003 c 111 s 106; 1987 c 346 s 3
Official source: Washington State Legislature. Reproduced from public-domain Washington statutes; confirm against the official source for the current text. Not legal advice.