How to create an external Slack channel, step by step

An external Slack channel is a channel you share with people at another company, through Slack Connect. Each company stays in its own workspace and only sees the channels you share. Setting one up takes a couple of minutes once you know the steps and the settings that can block them, so this guide covers both.

Before you start

Your company needs a paid Slack plan to invite another company to a channel. The other company does not: accepting is free, and you are notified when they join. Some free workspaces cannot use Slack Connect channels at all, though, so check with your contact if they are on a free plan.

Settings can get in the way too. Your admins can restrict who can invite people from outside, and they may need to approve what you send. If the option to add external people is missing, that is usually why, so ask an owner or admin before you troubleshoot further.

Decide who to invite first. Send the invitation to the person who will own the relationship on their side, using the work address they use for Slack. Inviting a shared inbox or a personal email address is a common reason an invitation never gets accepted, because nobody who can accept it ever sees it.

If the person is a freelancer without their own Slack workspace, a guest account may suit them better than a shared channel. Our comparison of Slack Connect and guest accounts explains the difference.

Create a new external channel

Create the channel as you would any other, then share it from its settings. A new channel starts with no history, which is usually what you want for a customer or partner.

1. Create a channel and give it a clear name, such as ext-northwind.
2. Open the channel and click the channel name in the header.
3. Select the Settings tab.
4. Under Slack Connect, click Add people.
5. Enter the email address of your contact at the other company, then click Add.
6. Choose An external organization, then click Next.
7. Choose whether they can post only, or post and invite others, then click Next.
8. Add a short note if you like, then click Send Invitation.

For customers, post only is the safer choice. It keeps the guest list in your hands, and you can always add their colleagues for them. Once you have sent the invitation, tell your contact to expect it, because an unexpected email from Slack is easy to ignore.

Share a channel you already have

You can share an existing channel by following the same steps from step two. Before you do, scroll back through it. The other company will be able to read the channel's history, not just what is posted after they join. Anything your team wrote about the customer, their pricing or their bugs becomes visible to them.

Some channels cannot be shared at all. Slack does not let you add external people to #general or #all-companyname, so create a dedicated channel instead. As a rule, share an existing channel only when it was always about the work you are doing together. If it holds internal discussion, start a fresh one and link to anything the partner needs.

What happens after you send it

Depending on each company's settings, people may need admin approval to accept your invitation, and your own admins may need to approve sending it. If nothing happens for a day, an approval is the usual reason.

Once the other company accepts, they choose how the channel appears on their side. Each workspace can give it its own name and can make it private on their side, whatever you chose on yours. You will see their people marked as external, with a square status indicator next to their names.

You do not need a new invitation for every colleague on either side. Your own teammates can join the channel like any other. If you chose post and invite, your contact can add their colleagues. If you chose post only, ask them who should be there and add them yourself from the channel settings. Either way, the channel's member list shows which company each person belongs to.

They only see the channels you share, never the rest of your workspace. Slack is explicit that you do not have to give people access to your whole workspace, just the channels you collaborate in.

When the invitation doesn't work

Most stuck invitations come down to an address, an approval or a plan. This table covers the common cases.

If you sent the invitation to the wrong person, you can revoke it as long as it has not been accepted, then send a new one. When the other side sees an error while accepting, our guide to Slack Connect invitations that cannot be accepted walks through the usual messages and fixes.

Set the channel up in the first hour

The first hour decides whether the channel becomes useful or turns into another inbox. Do these five things while the invitation is fresh.

First, keep the name consistent. A fixed prefix such as ext- makes every shared channel easy to find and sort. Second, set notifications for the channel to all new messages for whoever covers the account, so a question does not wait for someone to scroll past it. Third, create an internal companion channel, such as int-northwind, for the conversations the customer should not see.

Fourth, pin a short note that says who answers and when. Here is one to adapt:

Welcome to #ext-northwind, the shared channel between Northwind and our team.Who answers: Priya (account owner) and Sam (backup), weekdays 9am to 6pm London time.Please reply in threads, so each question stays in one place.Urgent issues: start your message with URGENT and mention @support-oncall.

Fifth, if you would rather talk to one person privately, you do not need a new channel for that. Once you share a channel, you can start a direct message with them through Slack Connect without a separate invitation.

From there, the work is keeping the channel responsive. Our Slack Connect guide covers running shared channels day to day. Our playbook on Slack for customer service covers ownership, response targets and coverage when a team supports many customers this way.

Questions people ask