One of the neat features of Office 365 is the ability to use instant messaging (IM) capabilities within the Exchange Online Office Web App (OWA). Customers can leverage their existing Lync on-premise deployment to provide this functionality. To integrate on-premise Lync Server with Exchange Online, administrators must first configured a Shared SIP Address space. Next you would configure federation between O365 and Lync on-premise and ensure that DNS is configured so that the Lync Edge server can route to O365.
On the Lync front end server, use the Lync Server Management shell command Get-CsAccessEdgeConfiguration to check to see if federated users are allowed. Look for the settings AllowedFederatedUsers and EnablePartnerDiscovery and confirm they are both set to “true”. If the settings are “false” use the command Set-CsAccessEdgeConfiguration to modify the setting.
Next, you want to confirm that the hosting provider for O365 is configured. Use the Lync Server Management shell command Get-CsHostingProvider. If your customer is using Lync Online and Exchange Online, you should see the output similar to this:
Lync Online Settings:
Exchange Online Settings:
|Identity||: Exchange Online|
|Name||: Exchange Online|
If the hosting provider is missing, it can be added using the following command:
New-CsHostingProvider -Identity “Lync Online” -Enabled $True -EnabledSharedAddressSpace $True -HostsOCSUsers $False -ProxyFQDN “sipfed.online.lync.com” -IsLocal $False -VerificationLevel UseSourceVerification
New-CsHostingProvider -Identity “Exchange Online” -Enabled $True -EnabledSharedAddressSpace $True -HostsOCSUsers $False -ProxyFQDN “exap.um.outlook.com” -IsLocal $False -VerificationLevel UseSourceVerification
Confirm DNS SRV Records both internally and externally. In CMD prompt execute: nslookup -type=all _sipfederationtls._tcp.mydomain.com
If you find that the integration is not working and logging on the client shows the following error:
Confirm that the SRV Record _sipfederationtls._tcp.mydomain.com is created both internally and externally.
You will also want to ensure that your firewall is not blocking access to all the Lync Online and Exchange Online IP addresses. https://technet.microsoft.com/en-us/library/hh373144.aspx
If you get the error: SIP/2.0 400 Missing correct Via Header in the edge server; confirm that there is not firewall or reverse proxy between the internal Edge server NIC interface and the front end server.