Yes it should work on normal Nextcloud / Owncloud instances just fine.
In reply to your doubts about using a free service:
I also use some other services at TransIP and I’ve been a customer for years, so I am not that much afraid of losing data. Generally, I’ve never experienced any real problems.
In this case, I do not even worry a lot about stability, although my experience has been great using Stack, because:
- MIAB will verify and warn that backups aren’t run properly.
- I’ll then still have local backups, this is only for offsite backup.
- It’s easy to migrate those to another service.
- Therefore, it would only be a problem if both my mail server, which is at another provider, and the stack storage would stop functioning at the same time.
- Even a hack wouldn’t bother me that much, since all data will still be strongly encrypted.