Transactional mail through an authenticated sending service, with a delivery log — so that "the email never came" becomes an answerable question.
SPF, DKIM and DMARC configured and verified. Sent through a relay rather than straight from the server, because otherwise the spam folder decides.
Accepted, delivered, opened, rejected — traceable per message. A bounce is an event with a reason, not a guess.
Order confirmation, password link, invoice: one template per occasion, in both languages, from the same data as the interface.
Sender on your domain, not ours. The reputation and the delivery rate are yours and move with you.
Briefly describe your case. We will tell you whether this building block covers it — and if not, what does.