Trumail

Trumail is a free and open source email validation/verification system. It is available in three forms, the Golang client library verifier for use in your own Go projects, a public API endpoint (more info: https://trumail.io), and a public Docker image on DockerHub (see: https://hub.docker.com/r/sdwolfe32/trumail/).

Our own API endpoint allows up to 1RPS per IP. This is to prevent abuse and to leave the tubes open for other users. If you perform requests in excess of the specified rate-limit a 429 Too Many Requests will be returned instead.

NOTE: It is highly recommended (due to potential heroku IP blacklisting resulting in failed validations) that you host the service yourself either using a Docker image or by forking and serving this project on your own instance. However, self-hosting Trumail requires bidirectional communication on port 25 which most residential ISPs restrict. AWS and Digitalocean both allow this.

Using the API (public or self-hosted)

Using the API is very simple. All that's needed to validate an address is to send a GET request using the below URL with one of our two supported formats (json/xml).

trumail.io/{format}/{email}

Using the library

package main

import (
	"log"

	trumail "github.com/sdwolfe32/trumail/verifier"
)

func main() {
	v := trumail.NewVerifier(20, "YOUR_HOSTNAME.COM", "[email protected]")
	res := v.Verify("[email protected]")
	log.Println(*res[0])
}

Running with Docker

docker run -p 8000:8000 -e [email protected] sdwolfe32/trumail

How it Works

Verifying the deliverability of an email address isn't a very complicated process. In fact, the process Trumail takes to verify an address is really only half that of sending a standard email transmission and is outlined below...

First a TCP connection is formed with the MX server on port 25.

HELO my-domain.com              // We identify ourselves as my-domain.com (set via environment variable)
MAIL FROM: [email protected]     // Set the FROM address being our own
RCPT TO: [email protected] // Set the recipient and receive a (200, 500, etc..) from the server
QUIT                            // Cancel the transaction, we have all the info we need

As you can see we first form a tcp connection with the mail server on port 25. We then identify ourselves as example.com and set a reply-to email of [email protected] (both these are configured via the SOURCE_ADDR environment variable). The last, and obviously most important step in this process is the RCPT command. This is where, based on the response from the mail server, we are able to conclude the deliverability of a given email address. A 200 implies a valid inbox and anything else implies either an error with our connection to the mail server, or a problem with the address requested.

The first 3 command steps above process happen here. Deliverability is checked here. Transaction is cancelled (QUIT) and the connection is closed here.

The BSD 3-clause License

Copyright (c) 2017, Steven Wolfe. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

• Neither the name of Trumail nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.