I have been using Mail In a Box for about a year now and I am very happy with it. One annoying snag I bump into from time to time involves DNS records. My MiaB hosts email for five different domains, and and on two of them I have about a dozen subdomains for a number of other services hosted elsewhere.
Periodically I need to change the IP addresses for a dozen records, and right now I have to delete every single one and then manually re-add every single one. It is maddening. It would be incredibly helpful to be able to select a group of records and update them all at the same time, or at the very least put and  button next to [delete] for each record so I don’t have to delete them and re-add them.
I have looked into scripting this via the API but that is not a tenable solution for me. This should be able to be achieved entirely though the WebUI.
If there is a bug bounty for this project I will gladly contribute towards this particular enhancement. It would make a world of difference for me.
I assume you will need to run the dns_update.py script (but don’t actually know). After making the update to custom.yaml, I would try going through the web interface and making another DNS change to have it run the DNS update.