Teams users can now chat to Skype users by using their email address and vice versa.

You can search for Skype users by typing their email address (not Skype ID or phone number)

Some features are not available to external users such as emojiis, screen sharing, @mentions, schedule a meeting and attachments. You can use chat, audio call and video call with Skype users.

In Skype, full functionality is also not available but you can use chat, audio call and video call.