Open States seems to have most/all CA state senators’ email addresses with a sen.ca.gov domain.
I sent email to 4 CA senators using that domain and 3 of them bounced. I found that https://calrta.org/wp-content/uploads/CA-Legislator-Capitol-Contact-Info-2018-1-18.pdf lists the domain of all but one CA senator as senate.ca.gov. I re-sent all 4 emails with a senate.ca.gov domain and none bounced.
Also, I got a bounce from CA Assembly Member Randy Voepel which is listed by Open States with an email of email@example.com. That PDF document indicates the address as firstname.lastname@example.org.