I have an accounting practice here in Tucson. Last year I did an Estate return for a client that had never lived in California but their kid, who was the Estate representative, lived in CA and had mail delivered to him there. The FTB sent the estate a letter demanding CA tax. When I wrote back and explained that the ONLY reason I could think of that CA showed up anywhere in the whole process was the receipt of mail by the representative the situation was resolved in the Estate’s favor. Getting it resolved required that extra step and the ONLY reason I can think of for CA getting involved was the mailing address which, frankly, is rather concerning because how would CA know that person X, living in CA, received mail for person B, living in Arizona?
ZEY HAVE ZERE VAYS!...........................
..probably because every piece of mail is scanned for addressee and sender, so they collect that info and share with the IRS or any govt entity... ymmv