nuxt-mail working in dev but not in production

I configured nuxt-mail in the nuxt.config.js file like (My EMAIL_HOST env var is the domain of my mail server):

mail: {
    message: {
        from: process.env.EMAIL_USERNAME,
        to: process.env.EMAIL_RECIPIENT,
    },
    smtp: {
        host: process.env.EMAIL_HOST,
        port: parseInt(process.env.EMAIL_PORT, 10),
        secure: true,
        auth: {
            user: process.env.EMAIL_USERNAME,
            pass: process.env.NUXT_EMAIL_PASSWORD,
        },
    },
},

And I send it in my form like this:

const mail = useMail()

function sendMail() {
    const emailContent = `
        <div style="font-family: Arial, sans-serif; line-height: 1.6;">...</div>
    `;
    mail.send({
        from: `${firstname.value} ${lastname.value}`,
        subject: subject.value,
        html: emailContent,
        replyTo: email.value,
    });
}

This works fine in development mode and I receive all mails correctly. However after building, I get the following errors in my console:

http://localhost:3000/mail/send 500 (connect ECONNREFUSED 127.0.0.1:465)

Uncaught (in promise) Error: connect ECONNREFUSED 127.0.0.1:465 at Object.send

The production server is a VPS using PM2 as the process manager, but the build already does not work locally, so I don't think that's the issue.

Does anyone have an idea how to solve this?

Thanks a lot.