Office 365 has lots of redundancy built into their network , which covers you automatically from Hardware, Software, or Corruption, so you are somewhat automatically protected from failure.
Some companies don’t trust what they can’t see with the cloud so they like locally hosting their data.
Office 365 Retention Policies
You can add a “Forever” retention policy to your Office 365 tenant which means items can never be deleted for free. Officially this is part of the Office 365 Enterprise License ( E1-E5) However even on the Business Essential / Premium Products you can still enable this and lookup deleted emails.
Why Backup is different from Retention
Say for example you have a retention policy enabled. A user re-arranges a load of emails from one folder to another folder and so on , then down the line wants to revert all her changes. You cannot use the retention policy to restore these as they have never been deleted. This is where you need a backup of the previous day or hour when you have a snapshot of that folder to restore too.
Veam
If you are backing up Virtual machines you probably will be using Veeam to an offsite and onsite location.
Veeam offers a free Veeam Community Edition for 10 Users or Less ( No Support ) which will integrate into your existing infrastructure
Synology NAS
If you still have on-premise servers you are probably using an Onsite NAS to back these up to.
If you are using a Synology NAS , any 64-bit NAS with DSM6.1 or later with 2GB of RAM or more, supports “Active Backup for Office 365” package on Synology. This allows to backup drive, mail, contacts and calendar… items. For Free!
https://www.youtube.com/watch?v=pBK0pI7qF6A&feature=youtu.be
supported models: https://www.synology.com/en-us/dsm/packages/ActiveBackup-Office365
Just because you have a backup it is not saying there won’t be any downtime to your company if a service goes down or an error occurs that needs to be restored from. Backups usually have a Restore time of 4-24 hours depending how much data needs to be restored.
If you are looking for a Zero Company downtime solution you will want a service such as Mimecast Continuity