The relay you already know how to use.

Already have a mailer? Change four settings and you are sending through Drin. No rewrite, no SDK — point any SMTP client at smtp.drin.run, use your API key as the password, and get the same deliverability as the REST API.

# point any SMTP client at Drin
host      smtp.drin.run
port      465   # TLS — or 587 for STARTTLS
username  drin
password  $DRIN_API_KEY   # your API key
from      hello@drin.run

# Nodemailer example
const t = nodemailer.createTransport({
  host: "smtp.drin.run", port: 465, secure: true,
  auth: { user: "drin", pass: process.env.DRIN_API_KEY }
});