# Nodemailer MJML i18next Compiler > Nodemailer compile plugin that renders MJML templates with Handlebars and i18next translations to produce responsive HTML emails from MJML. This file points LLMs to concise, high-signal references for using the library. Core flow: Handlebars renders data and translations into MJML; MJML compiles to responsive HTML; the Nodemailer compile plugin assigns the result to `mail.data.html` and resolves a translated subject when configured. Templates are resolved by trying `.mjml.hbs`, `.hbs.mjml`, `.mjml`, then `.hbs`. i18n defaults to filesystem-backed `i18next` loading from `locales//.json`. Use `{{t "ns:key"}}` or `{{__ "ns:key"}}` in templates; locale comes from `mail.data.locale`. Important notes: - The plugin runs in Nodemailer’s compile phase (`transporter.use('compile', ...)`). - `strict` throws on MJML errors; otherwise errors are exposed at `mail.data.mjmlErrors`. - Subjects: set `mail.data.subject`, or use `mail.data.subjectKey`, or enable `autoSubject` (default) to use `: