Error: A partials dir must be a string or config object in handlebars
Looks like a recent change to express-handlebars caused this issue, someone posted a fix here https://github.com/yads/nodemailer-express-handlebars/issues/22
Or
I guess you could just go back to a version that doesn't have this issue, at least until it is fixed.
I managed to get my code working, posting in case it helps out. I had to add the partialsDir to my handlebarOptions where I didn't have the field before:
const handlebarOptions = { viewEngine: { extName: '.hbs', partialsDir: 'src/path', layoutsDir: 'src/path', defaultLayout: 'email.hbs', }, viewPath: 'src/path', extName: '.hbs',};transporter.use('compile', hbs(handlebarOptions));Hope this helps.