To integrate Lync On-premise with Exchange Online UM, we can check the following configuration:
1. Verify Edge Functionality
A working Edge server is a Requirement for Lync Server On-Premises to work successfully with Exchange Online UM. Confirm the following in the environment:
Verify that a Lync user can sign-in remotely through the Lync Edge Server.
Have an internal Lync user send an IM to an external federated user.
Make sure internal Lync users can establish audio calls with remote users and federated users through the Lync Edge. Note The call flow between the Front End, Edge and Exchange Online UM is similar to the call flow between internal and federated users. If that isn’t working, then integration with Exchange Online UM will not work either.
Suggestion: The best way to do this is to apply an trail account of Office 365 E3 and then ask your customer to add this trail account O365 domain to their allowed list and then try and initiate IM session, audio calls with the Lync users in this Office 365 trail domain.
Link to apply an E3 trail account:
http://products.office.com/en-us/business/office-365-enterprise-e3-business-software
2. Check Lync Server On-Premises Configuration
Get-CsHostedVoicemailPolicy
The Destination attribute should always be pointing to exap.um.outlook.com. The Organization attribute should point to either the default O365 tenant domain (contoso.onmicrosoft.com) or the company’s domain (Contoso.com).
Important: The domain name of your company that is used HAS to be an accepted authoritative domain in Exchange Online. You can check If the domain entered by the customer is an authoritative domain by connecting to Exchange Online Remote PowerShell. For more information, see Manage accepted domains in Exchange Online on TechNet.
Get-CsHostingProvider
The ProxyFQDN attribute should always be pointing to exap.um.outlook.com for every customer using Exchange Online UM. The Enabled and EnabledSharedAddressSpace parameters should always be set to TRUE.
Get-CsAccessedgeConfiguration
The RoutingMethod attribute should be set to UseDnsSrvRouting.
Get-CsExUMContact
LineURI should match the number configured for the Subscriber Access number in the Exchange Admin Center. Hosted Voicemail Policy should be populated and IsSubscriberAccess should be set to TRUE.
3. Check Lync Server On-Premises Edge configuration
Check Lync Edge. The internal network interface should not have a default gateway
Check Lync Edge. The external network interface should use public DNS and not the internal DNS server.
Perform NSLookup/ Running NSLookup from the Lync Edge Server against the federation SRV record (_sipfederationtls._tcp.domain.com) should resolve correctly to the Lync Edge Server public IP address of the Access External Interface of the Edge Server.
Check internal DNS server. Also make sure that in internal DNS server. _sipfederationtls._tcp.<domain> is pointed public IP address of the Access External Interface of the Edge Server. If DNS records are changed, please make sure the DNS cache is refreshed.
Check Static Routes. Remove any configured static routes configured in Lync. Run Get-CsStaticRoutingConfiguration and look for any routes that may be interfering.
Check CMS Status
Make sure the replication status between the Front End and Edge server is good. Run Get-CsManagementStoreReplicationStatus and verify that both are up to date.
4. Check Office 365 Exchange Online Configuration
a UM Dial Plan or make sure one is created already
Make sure the UM Dial Plan type is set to SIP URI.
Verify the E.164 Routing Number in the Exchange Admin Center. When creating the Exchange UM Dial Plan in the Exchange Admin Center (or PoweShell), make sure the E.164 routing number is assigned so users can dial in to retrieve their voicemail. The E.164 routing number should match the number you assign to the ExUM Contact Object on-premises.
Make sure a user is enabled for UM and the UM policy is assigned.