Documentation

SMTP.

For apps that cannot call an API: WordPress, Laravel, Rails, Django, Supabase Auth, and anything with an SMTP settings screen.

Settings

Setting	Value
Host	`smtp.mailtruss.com`
Port	`587` with STARTTLS (recommended), or `465` with TLS
Username	`mailtruss` (any value works; the key identifies you)
Password	A Mailtruss API key. A sending-only key is enough.
Encryption	Required. Sign-in is refused on an unencrypted connection.

Mail sent over SMTP is an API send: the same domain checks, quota, suppressions, test addresses, delivery trace, webhooks and logs. It appears under Emails like any other message.

.env

1MAIL_MAILER=smtp
2MAIL_HOST=smtp.mailtruss.com(highlighted line)
3MAIL_PORT=587
4MAIL_USERNAME=mailtruss
5MAIL_PASSWORD=ms_live_...        # a Mailtruss API key(highlighted line)
6MAIL_ENCRYPTION=tls
7MAIL_FROM_ADDRESS=hello@yourdomain.com

1# config/environments/production.rb
2config.action_mailer.delivery_method = :smtp
3config.action_mailer.smtp_settings = {
4  address: "smtp.mailtruss.com", port: 587, user_name: "mailtruss",(highlighted line)
5  password: ENV["MAILTRUSS_API_KEY"], authentication: :plain, enable_starttls: true,
6}

1EMAIL_HOST = "smtp.mailtruss.com"(highlighted line)
2EMAIL_PORT = 587
3EMAIL_HOST_USER = "mailtruss"
4EMAIL_HOST_PASSWORD = os.environ["MAILTRUSS_API_KEY"](highlighted line)
5EMAIL_USE_TLS = True

1import nodemailer from "nodemailer";
2
3const transport = nodemailer.createTransport({
4  host: "smtp.mailtruss.com", port: 587, requireTLS: true,(highlighted line)
5  auth: { user: "mailtruss", pass: process.env.MAILTRUSS_API_KEY },
6});
7await transport.sendMail({ from: "hello@yourdomain.com", to: "ana@example.com", subject: "Hi", text: "Sent over SMTP." });

How SMTP mail is handled

The From address must be on a domain you have verified, as with the API. Sending to the test addresses works before any domain is verified.
Recipients come from the SMTP envelope. Addresses you send to that are not in the To or Cc headers are delivered as Bcc and stay hidden.
Up to 50 recipients and 18 MB per message, attachments included.
If your app retries a message it already sent (same Message-ID), it is not sent twice.
Tag messages with a header: X-Mailtruss-Tags: category=billing, plan=pro. Threading headers (In-Reply-To, References) and List-Unsubscribe are passed through.

Try it with swaks

1swaks --server smtp.mailtruss.com:587 --tls \
2  --auth-user mailtruss --auth-password "$MAILTRUSS_API_KEY" \
3  --from hello@yourdomain.com --to delivered@mailtruss.test

Errors

Reply	Meaning	What your app should do
`535`	The API key is wrong or revoked.	Fix the password.
`550`	Refused for good: unverified domain, suppressed recipient, invalid message.	Do not retry; the reply says why.
`552`	Too large, or the monthly limit is reached.	Upgrade, or wait for the next month.
`451 / 452`	Temporary: rate limit, daily limit, or a brief problem on our side.	Retry later (mail servers do this automatically).