https://www.csoonline.com/article/3292578/california-consumer-privacy-act-what-you-need-to-know-to-be-compliant.html
There is also a need to make sure data is being appropriately stored by the service provider since you have a "duty to implement and maintain reasonable security procedures and practices appropriate to the nature of the information to protect the personal information" [1].
I'd start by digging into how the mail provider is approaching compliance and security and whether they are planning to get certified.
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[0] Section 999.314 of the proposed regulations from AG https://hq.services/blog/ccpa-proposed-regulations/#999.314
[1] Section 1798.150 of CCPA https://hq.services/blog/ccpa-full-text-with-amendments/#179...
Note, the above links are to a version of the regulation that my company formatted to be easier to read. The original versions are here if you'd prefer:
[0] https://www.oag.ca.gov/sites/all/files/agweb/pdfs/privacy/cc...
[1] https://leginfo.legislature.ca.gov/faces/billCompareClient.x...
A business shall be in violation of this title if it fails to cure any alleged violation within 30 days after being notified of alleged noncompliance.
https://leginfo.legislature.ca.gov/faces/billTextClient.xhtm...