Backup jobs with Microsoft Exchange items may end up with the warning message shown in both the Veeam Backup for Microsoft Office 365 console and the Veeam.Archiver.Proxy.log file.

User-added image1/20/2020 6:30:28 AM   62 (2600) Resolving group: 753da553-b4dd-45ad-a773-180aa920c887:00000000-0000-0000-0000-000000000000...
1/20/2020 6:30:28 AM 62 (2600) Group found: TestOwnerGroup
1/20/2020 6:30:28 AM 62 (2600) Resolving group mailbox (ID: 753da553-b4dd-45ad-a773-180aa920c887:00000000-0000-0000-0000-000000000000)...
1/20/2020 6:30:29 AM 62 (2600) Found group mailbox:
1/20/2020 6:30:29 AM   62 (2600) Warning: Failed to find group owner account




Impersonation is not possible if Office 365 groups (mail-enabled and security groups) do not have an owner.




Make sure to assign an owner to each of the Office 365 groups (mail-enabled and security groups) as described in this Microsoft article.