I have a Linode VPS and am happy to fire up another VPS to handle email exclusively. In fact, I already did and installed Mail in a Box as mail.mydomain.com. I have to say (being a developer with enough Linux knowledge to handle hosting and simple stuff) that nameserver setup is completely confusing. I should stop using Linode nameservers? If so, I should set up glue records and place that into NameCheap domain speci…
It sounds scary to set up glue records, but so is setting up all of the DNS records manually that you'd need for really good mail: MX, SPF, DKIM, and DMARC, and if you want secure DNS and/or mandatory encryption on the wire you'll want DANE records and zone signing.
Mail-in-a-Box wants to take over your DNS because it wants to take care of all of this for you. If you run your own DNS, it's still secure. An alternative is to use a new domain name.
Thanks for the feedback.
[I'm the guy behind the project.]