I just installed Veeam Backup for Microsoft Office 365. It was easy to install and set up. However, I find downloading of the mailboxes to be pretty slow. I am on a 5Mb connection and I am processing at under 20kb/sec. Also, it times out after 4 hours. I saw that I could change it to 8. I dont know if that will be long enough.
Veeam Backup and Replication - 22.214.171.1241
Veeam Backup for Microsoft Office 365 - 126.96.36.1997
VMware ESXi Essentials 6
Server 2012 R2 VM