I struggled quite some time trying to get the Namecheap DNS records to work with Mailgun. Some things that would’ve helped to know when I started: For debugging MX records you can use this tool, for debugging DKIM this one and finally for SPF record this tool.
One thing that was according to the DKIM checkup tool missing was the DKIM version entry, so I added also v=DKIM1 at the beginning of my DKIM record value. Additionally the Check DNS Records Now button on Mailgun is far from real-time so if the tools show green for your records just be patient – I did the mistake of moving too fast and ended up wasting time also on that.
Finally, if you want to enable tracking add an additional CNAME Record with the host email.mail (email.yoursubdomain) and the value mailgun.org.
|DKIM and SPF records in Namecheap for Mailgun|
|MX Record setup on namecheap for Mailgun|