How to verify Mandrill custom sending domain without a mail receiving client?

The Background

I am using Mandrill as my SMTP sending mail server. After setting up MX in my custom domain DNS, I am able to send emails through Mandrill.

However, when reading the email from Gmail client, there's always an "on behalf of" line showing. I understand this signature could be removed by setting DKIM and SPF Settings, and I did so on Mandrill backend.

The Problem

Here comes the funny part: Mandrill requires you to "verified domain" by sending you a email to that custom domain. However, I didn't have a backend application to receive the "Inbound email" by Mandrill. Since there's no other mail client provided by Mandrill, how could I verify the Sending Domain?

References

• Why am I seeing extra information next to the sender’s name? (by Google)
• How Do I Get Rid Of The 'On Behalf Of' Message That Shows For Some Recipients? (Mandrill)

I was having the same problem earlier. I had a web application running on a server. So I configured incoming mails on mandrill by adding some MX records, then creating a route for the same domain for a random address which points to one of the POST endpoints on my web application.

So, whenever someone sends an email to that address, I get a POST request on the web endpoint which I put in the control panel. Mandrill gives a confirmation url in the email body. So, by inspecting the logs, we can directly copy the url and paste it in the browser and the domain is verified.

You can delete the incoming domain in mandrill afterwards if you don't need it.