It doesn't detect the settings

Autodiscovery needs DNS SRV entries to be added for each domain. The legacy Exchange- and Outlook-specific way was a file at /autodiscover/autodiscover.xml but I don't know if email clients still use that.

I have to ignore the certificate warning

I'm not familiar with Stalwart but you should be able to use Let's Encrypt certificates.

I was using Veeam when my stack was on VMware, but after moving to Proxmox I've been unable to get the Veeam agent working properly for VM recovery.

I tried Proxmox Backup at one point, and while it did work for base VM backup, the interface and capabilities of it just don't stack up to Veeam in my opinion, and I'm more concerned about file backup than VM recovery as I can easily recreate anything in my stack through my documentation.

I'm actually glad you mentioned that because I do need to revisit it. The few times I did have to recover the VM from backup I was able to do so when my backup process was working, but I've thankfully not had any recovery situations in the past 2 or so years since moving to Proxmox. And recovery doesn't help in situations where your cert is expired which is usually my issue historically.

As for past email recovery, Mailcow does have documentation on recovering from a failed server\database, but I consider my personal deployment volatile since I'm only using it for alerting and mostly internal only services.

I would fully switch over to it if I had more personal time, and if I knew I could make my family comfortable with accessing it. But right now I feel the risk is too great to move anything personally or financially important over. In the event something bad were to happen to me, I'm the only one with knowledge on how to recover the environment and I don't need my family to take on that burden if I were to become incapacitated or forbid, pass away suddenly.