Veeam Backup for Office 365 - Invalid Exchange Server version

Since few days, Veeam’s support received this error from some end-users about Veeam Backup for Office 365 (release 1.0.0.912): “Invalid Exchange Server version” during backing up of mailboxes (Veeam Backup for Office 365 – Invalid Exchange Server version). The issue is confirmed, the quick fix is in place…

Warning message: “Processing mailbox xxx failed with error: Invalid Exchange Server version“.

Some more info from logs (source: Veeam Forum):

8/25/2017 1:46:08 AM 13 (6196) Adding 1 mailboxes in processing…
8/25/2017 1:46:08 AM 13 (6196) Processing mailbox: xxx…
8/25/2017 1:46:08 AM 13 (6196) Connecting to Exchange Web Services…
8/25/2017 1:46:08 AM 13 (6196) Host: outlook.office365.com
8/25/2017 1:46:08 AM 13 (6196) Requesting folder hierarchy changes…
8/25/2017 1:46:09 AM 13 (6196) No folder hierarchy changes
8/25/2017 1:46:09 AM 13 (6196) Preparing folders for items processing…
8/25/2017 1:46:09 AM 13 (6196) Error: Invalid Exchange Server version
8/25/2017 1:46:09 AM 13 (6196) Stack:
8/25/2017 1:46:09 AM 13 (6196) at Veeam.Ews.ExServices.GetExchangeServerVersion()
at Veeam.Ews.ExServices.get_ExchangeServerVersion()
at Veeam.Archiver.Source.MailboxActivator.PrepareFolders(IMailboxContext bind, ExFolder top, ExcludedFolders excluded, CancellationToken cancel)
at Veeam.Archiver.Source.MailboxActivator.DoMailboxWork(CancellationToken cancel)
at Veeam.Archiver.Source.MailboxAction.DoWork(CancellationToken cancel)
8/25/2017 1:46:09 AM 13 (6196) Mailbox processing failed: xxx

It looks like the version of back-end Exchange servers in Microsoft Office 365 has been quietly changed by Microsoft. The development team is aware of this issue and had been working towards the resolution.

Solution – Apply this patch :

First, stop all the jobs,
Stop “Veeam Backup for Microsoft Office 365 Service”,
Then, you can replace the original file: “Veeam.Ews.dll” file, located in “C:\Program Files\Veeam\Backup365” folder by this one: FIX 113114. You have to keep the same file name.
Note: Keep the source file as “Veeam.Ews_OLD.dll“,
Start “Veeam Backup for Microsoft Office 365 Service”,
Retry the job.