Give the post office a reasonable amount of time, about five business days, then call the hotline number at 18585655800 they will look you up on their system to see if it's been received.
You could drop it off personally at the Registrar of Voters office at 5600 Overland Ave #100, San Diego CA 92123. Or you could check online at sdvote.com and select verify receipt of mail ballot under the vote menu.
There are also Mail Ballot Drop Off locations at most libraries and at the ROV in Kearney Mesa. Also at any polling place on election day.
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