Using Lync server 2010 with office 365 email in the cloud

Question

We have a 5 year old install of Lync server 2010 in house that interacts with a local install of exchange 2008 via unified messenger. If down the road we want to try email in the cloud like office 365 can we still keep our local Lync server install? Thanks in advance.
This topic first appeared in the Spiceworks Community

Answer 1

I am reporting back with my solution.  I can now confirm that one can have Lync servers on-premises with Exchange Online using Office 365 and the Lync Phone Edition devices will work.  Contact search, calendar (although it only shows the day's
Lync meetings), and visual voice mail all work.
Summary of fix: AD FS certificates have to be issued by CAs that Lync Phone Edition trusts.
The problem was when the Lync Phone Edition came back and tried to log in through AD FS.  Since we had single sign-on with Office 365 set up before we even ventured down the Lync path, the certificates for AD FS weren't issued by a CA that Lync Phone
Edition trusted.  Getting new certificates solved the issue.  (They were issued by the same CA that did the "external web" certificate on the Lync Front End in case that matters.)
I tried hard to get the phones to trust the original certificate first, putting it in Active Directory using the
certutil -dsPublish method, putting the original CA on the Lync Web Services trusted list using
Set-CsWebServiceConfiguration.  But nothing seemed to work until I finally just gave up and got a new certificate issued.  I am now running without any certificates listed in Active Directory nor any explicitly listed in Lync's Get-CsWebServiceConfiguration
and it works great.
The Technet articles are woefully out of date when it comes to the trusted CA list, but here's a link to the list of trusted CAs (with the updated firmware): http://blog.schertz.name/2014/10/lync-phone-edition-and-public-certificates/