You're looking to track your sending's engagement, so you've enabled click tracking. However, the click tracking links, for some reason, will not resolve. Not to worry - we have a few common troubleshooting tips to help get your links up and running.

Check CNAME

The first step we recommend is to make sure you have the CNAME record for the sending domain properly configured. The tracking hostname should return mailgun.org for the US region, or eu.mailgun.org for the EU region. This can be easily checked in a terminal using a dig command (Linux/Mac) or an nslookup command (Windows). If the terminal scares you, you can always use a web-based tool like MX Toolbox. 

Note: The CNAME will not return if you've configured the CNAME as proxy/CDN, such as CloudFlare.

Dig: 

$ dig -t CNAME email.domain.tld +short

Nslookup: 

nslookup -q=CNAME email.domain.tld

You should receive the response "Mailgun Magnificent API" if you make an HTTP request to the base tracking hostname, like below: 

$ curl -s http://email.domain.tld
Mailgun Magnificent API

Check HSTS

Mailgun currently only supports HTTPS tracking links via the use of a configured CDN; more information on that in this article. The source of your issue might be a combination of this element of our system with your settings relevant to HSTS. HSTS tells browsers to enforce HTTPS connections to the domain.  This will result in the tracking links timing out.  The following curl request will quickly confirm if HSTS is enabled: 

$ curl -s -D- https://domain.tld/ | grep -i Strict
strict-transport-security: max-age=2592000; includeSubDomains; preload

You'll need to disable HSTS or use a different domain without HSTS for the tracking links to resolve. If you are unable to disable HSTS, or your use case requires HTTPS, you can check out the help article detailing the steps needed to enable HTTPS tracking links via the link above. 

Check Original Links 

Another element to check is verifying the original links are valid. The best way to do this is to grab the original MIME via either the API or the control panel, providing the message is less than 3 days old (the amount of time our system retains message bodies). We'll show you how to do this below:

1. First, log in to the Mailgun Control Panel (if you have not already done so).
2. Then, within the left-hand navigation pane, click the Sending option to expand its list of suboptions.
3. Next, click the Logs suboption.
4. Ensure that the domain in question is displayed within the Domain drop-down list towards the upper-right portion of the page.
   
   
5. In the search box, enter the Message-ID value.
6. If results are returned, find the row containing the details of the message in question and click the downward-pointing icon
7. Select the MIME option to view the full MIME.

Once you've obtained the MIME, you can inspect the links to see how they looked before they were rewritten to ensure the original links are valid.

Got Questions?

Mailgun by Sinch has answers! If you have any concerns or questions, please send us a Support ticket using the Support page within your Mailgun Control Panel.  Our Support Team will be happy to assist!