Tracking replies in Mailgun (or any other email service)

The proper way to do this is to use the Message-ID header because when a recipient replies to an email the Message-ID of the original email is included in the In-Reply-To header of the reply.

Let’s walk through an example.

When you send an email using Mailgun, Mailgun automatically creates a Message-ID and includes it in the response (you could also set your own custom Message-ID).

So if I send a message using the messages API:

curl -s -k --user api:key-3ax6xnjp29jd6fds4gc373sgvjxteol0 https://api.mailgun.net/v2/samples.mailgun.org/messages -F from='Excited User <me@samples.mailgun.org>' -F to='test <test@mailgunhq.com>' -F subject='Hello' -F text='Testing some Mailgun awesomness!'

Mailgun replies with:

"message": "Queued. Thank you.", "id": "<20120502235917.29259.30669@samples.mailgun.org>"

You can see it in a screen shot of my terminal:

Now when I open that email in an email client and look at the email source headers, you can see that Message ID:

Ok, now let’s see what happens when I reply to that email. I created a Route in Mailgun that posts my reply to a URL at Postbin. Of course, Mailgun dutifully posts all of the headers. As you can see below, the In-Reply-To header has the same Message-ID which you then can use to identify which specific email was replied to:

So that’s it, an easy way to track who’s replying to what.

Happy emailing!

Mailgunners