‘Lync can’t connect to Exchange. Your contacts list and conversations might have issues’

‘Lync can’t connect to exchange. Your contacts list and conversations might have issues’ I came across a problem with a customer who had been instructed to change their users default SMTP addresses as part of a larger company consolidation. This change has created a problem in Lync 2013 where the Lync client can no longer access the Exchange 2013 services such as Calendar and message history. Historically the smtp address and SIP URI were both user@contosocam.com The recent instruction requires them to add a further smtp address (contoso.com) to all user mailboxes and make this the default reply address. So now we have a user with a default smtp address of user@contoso.com and a Lync sip uri of user@contosocam.com. The additional default smtp address was added in Exchange and initially everything seemed to be fine. However, they found that following the change, when new PC’s were deployed and Lync profiles configured the Exchange services didn’t work and Lync configuration information in the client showed blank entries for the EWS services (both internal and external). The client also reports an error stating that ‘Lync can’t connect to exchange. Your contacts list and conversations might have issues’ A simple temporary fix was quickly found to change the default smtp address back to user@contosocam.com, delete the sign in info in Lync (both through client and delete the profile folder in windows user profile) – then sign into Lync. Exchange services will connect and you can then change the default SMTP address back to user@contoso.com – we don’t know if this cached info times out eventually but we had users working for 3-4 weeks...