We run Zimbra NE 5.x in a KVM-based virtual machine, and it's running perfectly for 2100 accounts, all connecting via the web interface (with just about every account logging in at 8am, and a couple of hundred being online concurrently throughout the day). Along with about 100 Blackberry devices connecting via BES (which also runs in a KVM-based VM on the same host). And a couple of hundred ActiveSync clients. And an unknown number of IMAP clients.
VMs have come a long way. With virtualised drivers for network and disk I/O paths, they're really not much slower than physical I/O paths. All it takes is a little time to benchmark, tune, and test.
And we don't even have that skookum of VM host hardware (several years old):
- 5U Chenbro case with 24 drive bays attached to a hot-swappable SATA backplane
- 1350W 4-way redundant PSU
- Tyan h2000M motherboard (S3992-E)
- 2x AMD Opteron 2220 CPUs @ 2.8 GHz (dual-core)
- 32 GB ECC DDR2-SDRAM
- 2x 3Ware 9650SE 12-port SATA-II RAID controller plugged into a PCIe slot
- 12x 400 GB WD SATA harddrives (RAID60 for bulk storage)
- 12x 500 GB WD SATA harddrives (RAID10 for fast storage)
- Intel PRO/1000MT 4-port gigabit NIC (PCIe)
- Tyan System Management Daughter Card (M3291) for remote management via IPMI
Not to mention, the best, easiest, fastest way to test something is to throw it into a VM. If it works, then you can consider leaving it in a VM or moving it to a physical machine. If it doesn't work, then you just trash the VM. No need to "waste" a physical host during the testing.
I'm sorry to hear you didn't have a good experience with Zimbra, and that you don't like VMs. But there's no need to trash things you don't like. There are lots of us running Zimbra without any issues ... even in VMs.