You can set the templates directory to anything in plugin.json, I think it defaults to just templates if you don't specify.

Link Preview Image nodebb-plugin-calendar/plugin.json at 4368fdca0ef99336fde9875ab600349a5b13e59c · pitaj/nodebb-plugin-calendar

Fully-featured calendar plugin for NodeBB. Contribute to pitaj/nodebb-plugin-calendar development by creating an account on GitHub.

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Them you match the path from views, so it would be templates/emails where you put them.