Good question, so I googled ;)
No stamp? No problem: Your mail-in ballot will get there anyway
Photo of Steve Rubenstein
Steve Rubenstein Oct. 27, 2016
Democracy is never easy — or cheap. And that includes the act of mailing in a ballot, a messy collection of thick cards that are weighty on the issues and just as weighty on the postal scale.
One stamp or two? Or maybe three? Is the envelope regular-sized or oversize? Does that cost extra? How much?
And what happens if you leave off the stamp entirely and drop a completed ballot into the mailbox stark naked?
The answer is — don’t worry. The mail will go through. All mailed ballots are delivered immediately to county registrars of voters, according to U.S. Postal Service spokesman Gus Ruiz, whether they are mailed with the proper amount of postage, or without any postage at all.
“It’s a little-known secret,” Ruiz said. “The Postal Service will always deliver a ballot, whether there is a stamp on it or not. We know how important this mail is, and we want to get it where it belongs as soon as possible.”
The issue is far from trivial. More citizens than ever are voting early. In 1964, 1 voter in 25 voted by mail in California. In the 2012 presidential election, 1 voter in 2 voted by mail. This election, registrars say, the percentage of mail-in voters can be expected to keep going up.
Some voters don’t need to affix any stamps — five of the nine Bay Area counties, including San Francisco, now supply mail-in voters with postage-paid return envelopes. But elsewhere, mail-in voters are asked to slap a stamp on the envelope, and many of them drop their ballots into the mailbox with insufficient postage or no postage at all.
“We don’t eat it,” Ruiz said. “The registrars of voters have agreed to reimburse us after the election for insufficient postage.”
more:
http://www.sfchronicle.com/bayarea/article/No-stamp-No-problem-Your-mail-in-ballot-will-10418630.php

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