An existing connection was forcibly closed by the remote host

[NorthGuard]

I just implemented Backup for M365, configuring the jobs as follows:

Mailbox job
- roughly 71 mailboxes
- selecting from a dynamic entra group where usertype = Member and only selecting Mail, Archive, Group Mail

Sharepoint-OneDrive job
- manually selected all Sites for Objects to Backup Up

Teams job
- manually select all Teams sites/channels

I was reviewing the results this morning and am seeing a bunch of mailboxes failing with the following error:
Processing mailbox <user> failed with error: An error occurred while sending the request.. Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host... An existing connection was forcibly closed by the remote host. :: 0:44:35

The Teams job is also failing with a different error:
9/5/2024 3:21:05 PM :: Failed to process team: <teamName>. Failed to process team files: <teamName> The SSL connection could not be established, see inner exception.. The remote certificate is invalid according to the validation procedure: RemoteCertificateNameMismatch, RemoteCertificateChainErrors :: 4:51:33

I was doing some preliminary research and am not yet seeing a clear fix for either of those issues.

Any suggestions would be appreciated!

[Polina]

Hi NorthGuard,

It could be a firewall or something else that is preventing the Veeam service from connecting.
The best would be to open a support case, provide our engineers with your logs, and let them check your network and settings.

Thanks!

[NorthGuard]

I don't think it is a firewall issue as it does backup quite a few mailboxes... just fails on others

[MuchachoNL]

Was this issue resolved? And if yes, how?

Currently finding myself in the same situation:
As per Veeam instructions there's 3 jobs.
- User-Based Services with roughly 1300 mailboxes and OneDrive accounts to process (4 TB) -> Dynamic Groups which have EOP1/2 and SP1/2 licensed users in them.
- Sharepoint & Teams with roughly 240 sites/teams to process (6 TB) excluded personal sites to be safe.
- Catch-all which has still about 200 items (shared mailboxes, resource mailboxes, etc)

The Catch-All is succeeding perfectly, runs in about 7,5 hours now, first one took 87 hours with a few failed objects.
The Sharepoint & Teams is a bit more fickle: first job took 144 hours and had maybe 14 failed sites, second job took 12 hours, and the third one is almost done after 2,5 hours at the time I'm writing this.
The User-Based is giving the most errors and I had to cancel the job after 203 hours with HEAPS of failed objects. As soon as I disabled this job, the message after "objects in queue" (Reason: organization throttling) for the other jobs disappeared.

All errors on the failed objects in User-based and catch-all have one thing in common: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host... An existing connection was forcibly closed by the remote host.
The leading message varies between An error occurred while sending the request and Email item data export from EWS failed.
Sharepoint errors are mostly about download time expiring on attachment backups.

I'm not sure if I should split the User-Based services job into mailboxes and OneDrive separately or use Backup Applications in the M365 tenant, and if so: how many.