Security deposit questions - urgent

[Alexandra West]

Hello, if tenant has not provided any mail forwarding address am I still required to return the security deposit? Is the onus on me to proactively ask her for her mail forwarding address if she failed to provide it upon move out? Also, I know about the 21 day rule - is that 21 business days or 21 calendar days?

note - there's a *lot* more to this story, I'm not just trying to keep a decent person's security deposit. I pulled an eviction case off the table in exchange for this person applying for State rental assistance funds and then she dipped. She didn't pay me a cent for a full year and used every lawful, albeit unethical, tactic in the book to legallt squat in my home in California for nearly a year in the name of Covid. I'm a cautionary tale.  

[Nathan Gesner]

If you don't have a forwarding address, then I believe you can send it to the last known mailing address. If they set a forwarding address with the post office, they should get it. If not, it will come back and you'll have proof that you complied with the time requirements.