"adsb" subdomain unavailable?

I’m bumping into a very strange issue. I want a subdomain of adsb.mydomain.com as an A record, but whenever I try and set that, I get an error with a blank message. I have tried with all the domains hosted on my instance and they all do the exact same thing. What’s going on here…?

Thanks!
John

@millerjs

Add an email user account with the name in the format of user@adsb.mydomain.com. That should work for you. Change the IP by adding an A record on the Custom DNS page (which is probably what you are trying to do now) to the correct IP for that subdomain.

For the record - the above is a workaround. I am unable to reproduce your issue.