Applies To: Office for business, Office 365 Admin, Office 365 Small Business Admin, Skype for Business, Skype for Business Online, Skype for Business admin center.

Do you want the people in your organization to use Skype for Business to contact people in specific businesses outside of your organization? If so, you and the admin in the other organization can set it up.

Enable business-to-business communications for your users

You must have admin permissions in Office 365 to do this.

  1. Sign in to Office 365 with your work or school account.

  2. Go to the Office 365 admin center preview > Settings > Services and add-ins.

  3. Choose Skype for Business.

    In the Office 365 admin center, choose Skype for Business.

  4. On the External sharing page, turn on the toggle for Let people in your organization contact people with Skype for Business in other organizations.

    Allow contacts with other organizations using Skype for Business

  5. On the same page, choose All domains are blocked except, and then add the name of the organization's domain that you want to communicate with.

    Choose which domains to allow or block

  6. Choose Save.

  7. Now make sure the admin in the other organization does these same steps in their Office 365 admin center. For example, in the All domains are blocked except box, their admin needs to enter the domain for your business.

  8. If you have a firewall, make sure you've added the following FQDNs: *, *, and

    That's it! Now your users can IM, hold meetings, and share desktops. And they can see who's online and available just by checking their contacts lists.

Tip: If you also want your users to be able to communicate with everyone who uses Skype, the free consumer app, see Let users contact other Skype users.

Turn off external communication for specific individuals
Let your users contact Skype for Business users in another organization (classic admin center)

Tips on setting up external communications

  • If the other organization is using Lync or Skype for Business Server on premises, they can learn more about setting up the required options by reading this TechNet article: Configuring Federation Support for a Lync Online Customer.

  • When two Skype for Business users in Office 365 are communicating with each other on separate domains, they can only use Skype for Business features (for example, video conversations or desktop sharing) that are turned on in both organizations.

  • If you change the setting from Only for allowed domain to Except for blocked domain, the list of domains isn’t kept.

  • If a Skype for Business user in your organization is put on an In-place or Litigation Hold, any IM conversations between that user and other Skype for Business or Skype users will be saved in Recoverable Items in their mailbox. These conversations aren't saved in the Conversations History folder in their mailbox.