Kamdjou, who is also Sublime's CEO, had spent his former career showing companies how he could break into their networks and avoid being stymied by email security products. Then he decided to work on a solution.
"I decided to build something that would stop me as an attacker," he said.
Business credit card issuer Brex had been using Material with Google inboxes, but after testing out Sublime, Brex switched, the startup's chief information security officer, Mark Hillick, told CNBC in an interview. There were many problem emails that Material allowed but Sublime did not, Hillick said.