If you wait long enough, you’ll find an HP 1/8 G2 LTO-5 SAS autoloader tape driver somewhere between $250-$350 on eBay. That gives you 12TB uncompressed or 24TB of hypothetically compressed storage. Then buy the absolutely cheapest SAS card like a Dell H200E (which goes for about $25) and you’re all set. Don’t forget the appropriate SAS cable.

And, this combo works perfectly with Veeam Community Edition.

Why bother with complexity? Just use a mail relay like SMTP2GO and all your potential problems will be solved regardless what self hosted email server solution you choose.

The other option is to enable Hyper-V, make a Linux VM, and install Docker on the Linux VM.

I wanted to like XCP-NG because it’s easy to use, but the limitation of 2 terabytes per VHD was the killer for me. I guess for most VMs you won’t need that much storage, but that was a deal breaker.

There may be some way to get around that limitation (which is an inherent issue with XCP-NGs storage stack) or use software RAID in an OS to create arrays of 2 TiB disks, but that’s a lot of effort for nothing.