I have not used MiaB with IPv6 so I can’t comment on how removing it will affect your setup. I wouldn’t think it would cause a problem, but I can’t guarantee that. I run my MiaB on DigitalOcean and I do not enable IPv6 without any problems.
The question for you is did your enabling of IPv6 fix your initial problem or was it something else you did or something that resulted from the initialization of IPv6 on your box.
I am new at this, so all of this is a learning experience.
I started wanting to run an email server at home on a Raspberry Pi.
I started with Citadel and ran that for about a year just for my own use. Trying to upgrade to a later version and a 3b+ had issues and so I started to look around.
I found a package out of NZ called SurgeMail and messed with it for a while. 5 users at home was free, but then 10 users was $100/yr and you were supplying the server. Issues with Charter/Spectrum Residential blocking/blacklisting caused me to look around some more.
Then I found MaiB and Linode. $5/mo. Spectrum Business was way more expensive.
0.30 was all there was. Installed that on a VPS. Struggled getting it working, but with the help of a nephew, I was up and running. Main issues were with getting the domain name registrar set correctly. I was over thinking the problem.
Linode VPS provide both IPv4 and IPv6. I worked at getting all checks on the status page in MiaB. It shows IPv4 and IPv6.
For some reason the IPv6 email sends were getting bounced because they were blacklisted at Spamhaus. I did not see that until I tried to use RoundCube to send emails. It was using IPv6 on the VPS.
Bottom line… Wisdom comes from experience, and experience comes from lack of wisdom. Circular problem.
Am I happy camper? You bet. Only thing on my wish list is quotas and that is going to be fixed.
My only question is… Will the upgrade that has this install over the top of my existing install?
EDIT: I am new to the email server world. I did industrial controls system integrations and control software. I have actually written code for the Intel 4004 by hand. I guess that dates me.