If you can't communicate with Lync users in other organizations, or with Skype users, first verify that your organization allows communication with external contacts. If necessary, contact your workplace technical support and refer them to this guided walkthrough for admins: Set up Lync Online external communications.
If your organization does allow external Lync contacts, here are some other troubleshooting steps you can take.
Lync external contacts still show "Presence Unknown" after 72 hours
Notify your workplace technical support. You can communicate with external Lync users only if the Lync admin in both organizations has turned on external communications.
Can't communicate with Skype contacts
Verify that the Skype user is signed in with a Microsoft account (formerly Windows Live ID).
If the Skype user has a custom Microsoft account (one that does not end in outlook.com, live.com, hotmail.com, or msn.com) you must format their IM address like this:
For example, if your Skype contact's Microsoft account is firstname.lastname@example.org, enter it as
If you still can't communicate with the Skype user after 72 hours, notify your workplace technical support, and provide them with this link: Set up Lync Online external communications.
Can't talk to two or more Skype users at the same time
This scenario isn't supported. However, you can set up a conference call with multiple Skype users by inviting them to a Lync Meeting.
Tip: Before you send the meeting invitation, click Meeting options in the ribbon, and under Permissions, click A new meeting space (I control permissions). That way the Skype users won't have to wait in the lobby before joining the meeting.
Can't communicate with AOL, Yahoo!, or Google Talk users
Lync 2013 for Microsoft 365 supports external Lync users, and Skype users signed in with a Microsoft account. Communication with other IM providers isn't supported.
I have a Skype issue that isn't listed here
Troubleshooting Lync-Skype Connectivity describes some of the less-common scenarios.