There’s no instructions in the setup guide on how to add namecheap glue records so I wrote up this super simple guide on how how to do it.
#Adding Namecheap glue and nameserver records for a mailinabox server
First you need to create the “glue records” by adding a new “Personal DNS Server” in the “Advanced DNS” tab of your domain.
Add both the “ns1.box” and “ns2.box” nameservers. (See here
for more information.)
You can view your added nameservers by using the search feature and specifying “ns1.box” or “ns2.box” nameservers:
Now all you need to due to add these personal nameservers as nameservers for your domain: