“Normal people” (those unfortunates who live in houses or apartments) receive their mail at the same address that is their legal (or “physical”) residence. The state where their home is located is automatically their domicile.
Nomads may not be at home or have a home but must, for legal purposes, have a legal residence.
Due to language in the Patriot Act, financial institutions (investment companies, possibly credit card issuers and banks) have a legal obligation to collect identifying information on their customers. This is known as Know Your Customer, or KYC. Many of these institutions have interpreted KYC to disallow mail forwarders, UPS stores, etc. as legal residences.
There is a houseless way to help the institution satisfy KYC. The guidance is given in FINRA regulations:
for an individual, a residential or business street address, or for an individual who does not have a residential or business street address, an Army Post Office or Fleet Post Office box number, or the residential or business street address of a next of kin or another contact individual… – FINRA1)