Can My Landlord Mail My Security Deposit Refund On The 21st Day, Or Do I Have To Personally Have It By Then?

California Civil Code Section 1950.5 provides that within 21 days of a tenant vacating the property the landlord must either give the tenant the full refund of their security deposit or give them an itemized list of deductions.  The landlord may deliver the refund by mail postmarked by the 21st day that the tenant vacated the property.