Mostly headroom. The 450 doubles the storage to 4 TB and is sized for around 600 mailboxes instead of 300, with the same RAID-1 mirroring, search, legal hold, and audit trail carried over from the 350. If your mail volume is closer to an enterprise footprint than a small office, the 450 gives you more runway before you'd need to upgrade again.

Yes. The Message Archiver supports federated search, so if you eventually add a second appliance for another office or a growing mailbox count, admins can still run one search across all of them instead of checking each archive separately.

No. Full message compression only reduces how much disk space each archived item takes up. Every message is indexed for full text search the moment it's archived, so search speed and e-discovery accuracy aren't affected either way.

No. Barracuda licenses the Message Archiver by appliance, not by mailbox. One flat cost covers the 450 regardless of how many of your 600 recommended users you're actually archiving, and every feature ships standard with no add-on modules.

Yes. The 450 is email platform agnostic, so it can archive from Exchange, Office 365, Google Workspace, Domino, and GroupWise at once, which matters if your company grew through acquisitions and never fully standardized on one mail system.