SMTP

SMTP Relay

Drop-in SMTP server for legacy apps. Send through Transmit without changing your application code. Just update your SMTP credentials.

How it works

1

App sends via SMTP

Your application connects to xmit-smtp using standard SMTP with TLS on port 587.

2

xmit-smtp receives

The open-source SMTP proxy authenticates using your Transmit API key as the SMTP password.

3

Proxied to REST API

The SMTP message is converted to a REST API call and sent to Transmit's API for processing.

4

Delivered via SES

Transmit delivers the email through AWS SES with full deliverability tracking, analytics, and bounce handling.

Capabilities

SMTP + TLS

Standard SMTP protocol with STARTTLS encryption on port 587. Compatible with every email client and framework.

Any Language or Framework

Works with Nodemailer, PHPMailer, smtplib, Laravel Mail, Django, Rails ActionMailer, WordPress, and any app with SMTP support.

Open Source (MIT)

xmit-smtp is fully open source under the MIT license. Self-host it, contribute, or audit the code yourself.

Full Email Support

HTML and plain text bodies, file attachments, CC/BCC recipients, custom headers, and reply-to addresses.

Laravel .env Configuration

env
MAIL_MAILER=smtp
MAIL_HOST=smtp.xmit.sh
MAIL_PORT=587
MAIL_USERNAME=api
MAIL_PASSWORD=xmit_live_your_api_key
MAIL_ENCRYPTION=tls
MAIL_FROM_ADDRESS="hello@yourapp.com"
MAIL_FROM_NAME="Your App"

Related features

Inbound

Inbound Email Processing

Receive, parse, and route incoming emails with webhooks, forwarding, or database storage. Per-address routing with wildcard support.

Webhooks

Email Webhooks

Real-time notifications for email events. Get instant delivery, bounce, open, click, and complaint data pushed to your endpoint.

Frequently Asked Questions

What is an SMTP relay?
An SMTP relay is a server that accepts outgoing email via the SMTP protocol and forwards it to the final delivery service. It lets legacy applications send email through modern infrastructure without code changes , just update the SMTP host, port, and credentials.
Do I need to change my application code?
No. If your app already sends email via SMTP, you only need to update the SMTP host, port, username, and password in your configuration. The xmit-smtp relay handles the conversion to Transmit's REST API automatically.
Is xmit-smtp open source?
Yes. xmit-smtp is released under the MIT license and available on GitHub. You can self-host it, inspect the code, or contribute improvements.
What ports are supported?
The SMTP relay listens on port 587 with STARTTLS encryption by default. This is the standard submission port recommended by RFC 6409 for authenticated email sending.
Can I send attachments via SMTP?
Yes. The SMTP relay supports file attachments, HTML and plain text bodies, CC/BCC recipients, custom headers, and reply-to addresses. Everything a standard SMTP client can send is supported.
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