Cal. Probate Code § 878

Unless otherwise ordered by the court, directed by the user, or provided in a trust, a custodian shall disclose to a trustee that is not an original user of an account the content of an electronic communication sent or received by an original or successor user and carried, maintained, processed, received, or stored by the custodian in the account of the trust if the trustee gives to the custodian all of the following: (a) A written request for disclosure in physical or electronic form. (b) A certified copy of the death certificate of the settlor. (c) A certified copy of the trust instrument, or a certification of trust under Section 18100.5, evidencing the settlor’s consent to disclosure of the content of electronic communications to the trustee. (d) A certification by the trustee, under penalty of perjury, that the trust exists and that the trustee is a currently acting trustee of the trust. (e) If requested by the custodian, any of the following: (1) A number, username, address, or other unique subscriber or account identifier assigned by the custodian to identify the trust’s account. (2) Evidence linking the account to the trust.