Outlook clients disconected

We have a simple exchange 2013 setup with one CAS server, one mailbox server and one archive server.
This morning we had a brief issue where outlook clients were showing as disconnected.
Restarting outlook on my machine solved the problem and it was showing as connected.
On mailbox server CPU and memory usage was high but no errors.
test-servicehealth and test-mailflow were ok.
What else can I check to find out what happened.
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Zacharia KurianAdministrator- Data Center & NetworkCommented:
Have you checked the event logs in your server?

Mal OsborneAlpha GeekCommented:
A basic connectivity issue will cause that, along with prompts for credentials. Any sort of cabling or switch problems?
yo_beeDirector of Information TechnologyCommented:
Was there a reboot of the CAS prior to this issue?
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Budhi WitonoCommented:
you can change basic authentication to ntlm authentication via ecp
Alexa JacksonDigital Forensic AnalystCommented:

This issue generally occurs when the public folder to which one or more Exchange 2013 mailbox database point to as the default public folder setting was deleted in ADSI Edit.

Get the issue cross checked by making use of the following command: -
Get-MailboxDatabase | FL name,PublicFolderDatabase

Open in new window

Let me know if this was the case. Then I may help you out with a suitable solution.
curious7Author Commented:
thanks all. I think the issue was on the CAS server.
I stopped processing requests because of the following error:
[RpcHttp] The number of outstanding requests for guard TargetBackend("server-name") has exceeded the max limit 150. Current request will be rejected.

https://arstechnica.co.uk/civis/viewtopic.php?f=17&t=1290197 article suggest to increase the http proxy (rpc and sync) max limits and then recycle MSExchangeSyncAppPool and MSExchangeRPCProxyAppPool in IIS manager.

Does anyone know if this will cause outage to email (external and internal)?
And would it mean for 1-2 minutes that these pools recycle, will external emails get bounced back as undeliverable.
We have mail marshall in front of it.
Alexa JacksonDigital Forensic AnalystCommented:

I think the external will not get bounced and triggering the pool to recycle would be required if the limit of 5000 in IIS is achieved.

curious7Author Commented:
I did the http proxy (rpc and sync) max limit increase and then recycle MSExchangeSyncAppPool and MSExchangeRPCProxyAppPool in IIS manager. Issue has not reappeared since then.

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curious7Author Commented:
Issue has not appeared since the  change
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