Okay, that helped!
I’m not quite sure why you have ns1.box and ns2.box pointed to MiaB. You’re not using MiaB DNS server correct? You’re using Zuver, right?
If that’s correct then in Zuver you would keep the nameserver to Zuver’s name server. If your’re having DNS problems I would suggest removing all records in Zuver. Fresh clean slate. Once you have all the records removed visit MiaB Admin area. MiaB/admin
Under system click on External DNS. Enter every record as is. I don’t know if Zuver allows for ipv6 AAAA records. If not, just skip those. I also skip the SSHFP records.
After you have all those records entered. Then in Zuver create another A record for Collabora.
Test it out.
Couple side notes. In the external DNS it has you entering an A record for your primary domain. If you have a website etc. you will want to change that IP and point it to your website etc.
When you are running LetsEncrypt this is on your Collabora droplet, correct? Not on Mail in a Box.
This is how I normally install Lets Encrypt on Ubuntu 16.04
sudo apt-get install letsencrypt -y
sudo letsencrypt certonly --webroot -w /usr/share/nginx/office -d office.hostname.com
If you are still having problems send me a private message with your email address. Tomorrow I can do a Skype session with screen share and fix it all up for you.
I install MiaB all the time for my clients. It no problem at all.