Troubleshooting Lync Online DNS configuration issues in Office 365 http://support.microsoft.com/kb/2566790 In addition, could you go to run the Lync Connectivity Analyzer and check whether the test result is successful?

So, I installed this PPA and upgraded pidgin-sipe. The rest of my settings are: Basic tab: username: user@company.com Login: COMPANY\user Password: <password> Advanced tab: Server: sipdir.online.lync.com:443 Connection type: Auto User Agent: UCCAPI/4.0.7577.314 OC/4.0.7577.314 (Microsoft Lync 2010) Authentication scheme: TLS-DSK Use single sign-on: Off

tox-prpl – Tox Protocol Plugin For Pidgin