Of course we cannot expect to find every font face available, so we did not expect it in first place. Our client was therefore quite happy to find their corporate font Noto Sans JP available. Oddly enough, when emails are opened under « strict » conditions, it falls back on serif (which, as we typography endorsers know, is quite the opposite of sans-serif). To avoid the contradictory impression (« they don’t even get close to their own corporate design ») we must unhappily decide to not use the corporate font.
We have not found any settings option for fallback fonts (meaning something like « Noto Sans JP », Arial, sans-serif), therefore I guess the fallback is set in Brevo’s font module.
This topic should be related to Typographies qui changent entre éditeur et mail réceptionné
PS: First-level email support was not really helpful by suggesting that recipients should install the main font on their computers, btw.