asked on

Connection problems to Exchange 2016

Hello
wehre using Exchange 2016 in DAG. Latest CU12 installed and running.
In front there is KEMP Loadbalancer VLM 200.
Since last week, we had strange issues with Outlook Connection for:

1. Outlook for MAC 2016 or 2019 -> Connection will be lost
or
1a. Password must be re-typed again
2. Outlook for Windows is connected but online search results in a error that server cannot be reached. But Outlook 2016 Windows can send and receive without any issues.
2a. Some Windows Outlook Users reports same as for MAC Outlook, but not confirmed yet.

So you can see on Outlook Mac 2016, with several connected Mailboxes to this Exchange 2016, that connections are loosing all the time and reconnecting shortly.
It looks like, that a limit on Exchange is throttling this.
But on Exchange, there is no information in logs about reaching any kind of a limit.

So why is Outlook Windows working, Outlook Mac not.
We contacted KEMP Enterprise Support. They don't see a fault in VLM 200.
On VLM 200 we see 3500 connections.

So on which limits in Exchange we're running here?
Thanks for help.
If more information is needed, please ask.

Attached Global Settings:
RunspaceId :
ThrottlingPolicyScope : Organization
IsServiceAccount : False
AnonymousMaxConcurrency : 1
AnonymousMaxBurst : 120000
AnonymousRechargeRate : 420000
AnonymousCutoffBalance : 720000
AnonymousCostThreshold :
BookingSelfServiceMaxConcurrency : 10
BookingSelfServiceMaxBurst : 500000
BookingSelfServiceRechargeRate : 1800000
BookingSelfServiceCutoffBalance : 3000000
ConsensusMaxConcurrency : 10
ConsensusMaxBurst : 500000
ConsensusRechargeRate : 1800000
ConsensusCutoffBalance : 3000000
SchedulesMaxConcurrency : 5
SchedulesMaxBurst : 500000
SchedulesRechargeRate : 1800000
SchedulesCutoffBalance : 3000000
EasMaxConcurrency : 10
EasMaxBurst : 480000
EasRechargeRate : 1800000
EasCutoffBalance : 600000
EasMaxDevices : 100
EasMaxDeviceDeletesPerMonth : Unlimited
EasMaxInactivityForDeviceCleanup : Unlimited
EwsCostThreshold : 50
EwsMaxConcurrency : 40
EwsMaxBurst : 300000
EwsRechargeRate : 1800000
EwsCutoffBalance : 0
EwsMaxSubscriptions : 5000
ImapMaxConcurrency : Unlimited
ImapMaxBurst : 3600000
ImapRechargeRate : 600000
ImapCutoffBalance : Unlimited
OutlookServiceMaxConcurrency : 27
OutlookServiceMaxBurst : 300000
OutlookServiceRechargeRate : 900000
OutlookServiceCutoffBalance : 3000000
OutlookServiceMaxSubscriptions : 5000
OutlookServiceMaxSocketConnectionsPerDevice : 9
OutlookServiceMaxSocketConnectionsPerUser : 12
OwaMaxConcurrency : 20
OwaMaxBurst : 480000
OwaRechargeRate : 1800000
OwaCutoffBalance : 0
OwaVoiceMaxConcurrency : 3
OwaVoiceMaxBurst : 75000
OwaVoiceRechargeRate : 375000
OwaVoiceCutoffBalance : 525000
PopMaxConcurrency : 20
PopMaxBurst : 3600000
PopRechargeRate : 600000
PopCutoffBalance : Unlimited
PowerShellMaxConcurrency : 18
PowerShellMaxBurst : Unlimited
PowerShellRechargeRate : Unlimited
PowerShellCutoffBalance : Unlimited
PowerShellMaxTenantConcurrency : Unlimited
PowerShellMaxOperations : Unlimited
PowerShellMaxCmdletsTimePeriod : Unlimited
ExchangeMaxCmdlets : Unlimited
PowerShellMaxCmdletQueueDepth : Unlimited
PowerShellMaxDestructiveCmdlets : Unlimited
PowerShellMaxDestructiveCmdletsTimePeriod : Unlimited
PowerShellMaxCmdlets : Unlimited
PowerShellMaxRunspaces : Unlimited
PowerShellMaxTenantRunspaces : Unlimited
PowerShellMaxRunspacesTimePeriod : Unlimited
PswsMaxConcurrency : 18
PswsMaxRequest : Unlimited
PswsMaxRequestTimePeriod : Unlimited
RcaMaxConcurrency : 100
RcaMaxBurst : 150000
RcaRechargeRate : 900000
RcaCutoffBalance : Unlimited
CpaMaxConcurrency : 20
CpaMaxBurst : Unlimited
CpaRechargeRate : Unlimited
CpaCutoffBalance : Unlimited
RcaSharedMaxConcurrency : Unlimited
RcaSharedMaxBurst : 600000
RcaSharedRechargeRate : 3600000
RcaSharedCutoffBalance : Unlimited
MessageRateLimit : Unlimited
RecipientRateLimit : Unlimited
ForwardeeLimit : Unlimited
DiscoveryMaxConcurrency : 2
DiscoveryMaxMailboxes : 5000
DiscoveryMaxKeywords : 500
DiscoveryMaxPreviewSearchMailboxes : 5000
DiscoveryMaxStatsSearchMailboxes : 100
DiscoveryPreviewSearchResultsPageSize : 200
DiscoveryMaxKeywordsPerPage : 25
DiscoveryMaxRefinerResults : 10
DiscoveryMaxSearchQueueDepth : 32
DiscoverySearchTimeoutPeriod : 10
PushNotificationMaxConcurrency : 20
PushNotificationMaxBurst : Unlimited
PushNotificationRechargeRate : Unlimited
PushNotificationCutoffBalance : Unlimited
PushNotificationMaxBurstPerDevice : 10
PushNotificationRechargeRatePerDevice : 6
PushNotificationSamplingPeriodPerDevice : 600000
EncryptionSenderMaxConcurrency : 200
EncryptionSenderMaxBurst : 4800000
EncryptionSenderRechargeRate : 18000000
EncryptionSenderCutoffBalance : Unlimited
EncryptionRecipientMaxConcurrency : 20
EncryptionRecipientMaxBurst : 480000
EncryptionRecipientRechargeRate : 1800000
EncryptionRecipientCutoffBalance : Unlimited
ComplianceMaxExpansionDGRecipients : 10000
ComplianceMaxExpansionNestedDGs : 25
SuiteMaxConcurrency : 20
SuiteMaxBurst : 480000
SuiteRechargeRate : 1800000
SuiteCutoffBalance : Unlimited
IsLegacyDefault : False
Diagnostics :
AdminDisplayName :
ExchangeVersion : 0.20 (15.0.0.0)
y
ObjectClass : {top, msExchGenericPolicy, msExchThrottlingPolicy}
WhenChanged : 07.05.2019 14:48:17
WhenCreated : 06.05.2019 15:00:51
WhenChangedUTC : 07.05.2019 12:48:17
WhenCreatedUTC : 06.05.2019 13:00:51
OrganizationId :

IsValid : True
ObjectState : Changed

Thanks

Jakob Digranes

Hi - there's no limits on connections in Exchange that would cause this. But there might be limits or insufficient resources in either server hardware og KEMP load balancer. I've been through several cases like this, either server were memory strapped og load balancer had issues.

Do you have multiple Exchange servers?
Are they located in the same SITE or some connected at DR-Site?

I'd try this:
- try to isolate servers and make KEMP (HLB) connect to only 1 EX server at the time. Is the issue still there? Maybe the error goes away when Exchange server 2 is disabled -> Exchange Server 2 have issues
- bypass load balancers and connect directly to Exchange servers. Exchange 2016 use DNS for connection - so just change your mail-exchange DNS records to point to servers directly. If using multiple Exchange servers, create multiple A-records pointing to all server. If the issue still appears - change DNS record to point to to just one server at the time.
- it might be different settings on servers, which would explain the credentials pop-up

Most likely this would tell you if the issue is located at KEMP or at servers. If you experience this issues when conneting to any of the servers, both with or without HLB - look in to network related issues.
FIrewall policies?
TCP TimeOuts?

a far fetch issue; TCP IDLE TIMEOUTS, Exchange and Outlook have 2 hrs TCP IDLE TIMEOUT, whereas HLB and firewalls might have 30 minutes. This would cause reconnects and Outlook that hangs ... But this should show for users connecting to multiple mailboxes or calendars, and are IDLE for a given amount of time.

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