Changes in the way your ballot is postmarked
Ballots must be postmarked on or before Election Day.
However, postmarks will now reflect the day they are processed at a processing facility, which may not be the day you dropped your ballot off at the post office, or deposited it in a postbox.
To be sure your ballot is counted:
Mail it as early as possible, up to a week before Election Day if possible
Request manual cancellation at your local post office on or before Election Day (this is free)
Purchase a certificate of mailing or send registered or certified (this costs extra)
For more information: Frequently Asked Questions on Voting by Mail from the Washington Secretary of State