On paper, moving from Slack to Teams is a line item in a Microsoft 365 rollout. In practice, the switch lives or dies on three unglamorous things: your outside collaborators, your message history, and the integrations nobody wrote down.

Plenty of companies are making this move in 2026, usually to consolidate on Microsoft 365 and cut a separate Slack bill. Microsoft even released a free tool to migrate Slack channels into Teams. The pitch is smooth. The reality is that a chat platform is where years of decisions, files, and workflows quietly accumulated, and not all of it comes across cleanly.

The switch itself is manageable. What trips teams up is discovering, a week after cutover, that direct messages did not migrate or that a critical Slack automation has no Teams equivalent. These questions surface those gaps while you can still plan for them.

Before switching from Slack to Teams, confirm three things. First, how external collaborators will work, since Teams handles guests and external access differently from Slack. Second, exactly what message history moves, because Microsoft’s free migration tool covers channel content but not direct messages, which need a third-party tool. Third, whether your Slack apps, workflows, and bots have Teams equivalents. Sort out guests, history and retention, and integrations before cutover, and the move is smooth; skip them and you find the gaps after everyone has already switched.

Start with a clear-eyed inventory of what the migration carries. Microsoft’s built-in Slack to Teams migration tool moves content from Slack public and private channels, including messages, files, and memberships, and it is free. That covers a lot of your shared history.

The gap is direct messages. The built-in tool migrates channel content, not one-to-one DMs, which is where a surprising number of real decisions and file handoffs live. Moving those requires a third-party migration tool and a separate plan. There are quirks in the channel migration too: a thread reply that was also posted to the whole channel can arrive in Teams as two separate messages. Knowing this before cutover changes how you set expectations with your team.

This is the first place Slack and Teams genuinely differ, so ask these before you invite anyone.

• How do our external collaborators map over? Teams separates guest access, where someone joins your organization as a guest, from external access, which is more like federation between organizations. Decide which model each Slack Connect partner or single-channel guest should become.
• Who can invite guests, and with what permissions? Guest invitations are an admin-controlled setting in Microsoft 365, so confirm the policy before people expect to add outsiders freely.
• What do guests lose or gain? A guest in Teams inherits a defined set of capabilities. Check that your outside partners can still do what they did in Slack.

If your admins hit invitation errors during setup, our guide to Microsoft 365 guest invite permission errors covers the common fixes.

History is both a continuity issue and a compliance one, so treat it as two questions.

• Which history do we actually need to keep? Separate channels you must preserve from noise you can archive. You may keep a read-only Slack export for reference rather than migrating everything.
• What is our plan for direct messages? Since the free tool skips DMs, decide whether to use a third-party tool, export them for reference, or accept the loss for low-value chats.
• How does retention change under Microsoft 365? Teams data falls under M365 retention and compliance policies, which may differ from your old Slack plan. Set retention deliberately rather than inheriting a default.

Integrations are the least visible part of the switch and the most likely to break a daily workflow. Audit them before, not after.

• Which Slack apps do we rely on, and do they have Teams versions? List every connected app and confirm a Teams equivalent exists, since parity is not guaranteed.
• Where do our automations live? Slack Workflow Builder flows do not carry over. Plan to rebuild them, often in Power Automate, and budget time for it.
• What about custom bots and webhooks? Inbound webhooks, slash commands, and custom bots need to be re-pointed or rebuilt for Teams. Identify the owner of each one now.

The same discipline applies to any tooling move. Our checklist on questions before you migrate a CRM is a good model for auditing integrations and data before a cutover.

The cost case is usually the reason for the move, so confirm it holds.

• Is Teams already covered by our licensing? Teams is bundled with most Microsoft 365 business plans, which is often the savings driver, but confirm your specific plan includes what you need.
• Who owns admin and governance? Teams governance runs through the Microsoft 365 admin center. Decide who manages policies, naming, and lifecycle before you scale up channels.
• How does this fit the wider 365 picture? If you are consolidating tooling, weigh it alongside the rest of the suite. Our comparison of Google Workspace versus Microsoft 365 helps frame that bigger decision.

• Have we mapped every external collaborator to guest or external access?
• Do we have a plan for direct messages the free tool will not migrate?
• Have we set Teams retention and compliance policies deliberately?
• Have we inventoried every Slack app, workflow, and bot, with a Teams plan for each?
• Have we confirmed Teams is covered by our current licensing?
• Have we named an owner for admin, governance, and integration rebuilds?

• Assuming everything migrates. Channels move with the free tool; DMs do not. Plan for the gap.
• Forgetting the automations. Workflow Builder flows and custom bots need rebuilding, not copying.
• Treating guests as an afterthought. External access is a real configuration decision, not a checkbox.
• Ignoring retention. Inheriting default M365 policies can keep too much or too little. Set it on purpose.

• The free Microsoft tool migrates Slack channels but not direct messages, which need a separate plan.
• Teams handles guests and external access differently from Slack, so map every outside collaborator first.
• Slack workflows, bots, and webhooks do not carry over; inventory and rebuild them before cutover.
• Confirm licensing coverage and name owners for governance and integration work.

Channel history does, through Microsoft’s free migration tool, which moves messages, files, and memberships from public and private Slack channels. Direct messages are not included and require a third-party tool or a separate export plan.

Yes. Microsoft released a free tool, available in the Microsoft admin center, that migrates Slack channel content into Teams channels. It became broadly available to commercial customers in 2026 and covers channels rather than direct messages.

Teams distinguishes guest access, where an external person joins your organization as a guest with defined permissions, from external access, which connects whole organizations. Slack’s guest and Connect models do not map one-to-one, so decide the right setup for each partner.

Not automatically. Some popular apps have Teams versions, but parity is not guaranteed, and Slack Workflow Builder flows, custom bots, and webhooks must be rebuilt, often using Power Automate. Inventory them before switching.

Often, because Teams is bundled with most Microsoft 365 business plans, so teams already paying for 365 drop a separate Slack bill. Confirm your specific plan includes the Teams capabilities you need before assuming the savings.

Direct messages and automations. People assume the migration carries everything, then discover DMs did not move and a daily Slack workflow has no Teams equivalent. Both are fixable with planning, but painful as surprises.

Before you announce a date, run the inventory: external collaborators, the history you must keep, direct messages, and every app, workflow, and bot with an owner beside it. Match each to a Teams plan, then set retention and guest policies on purpose rather than by default. The teams that switch smoothly are the ones that treated Slack not as a chat app to turn off, but as a system of record to migrate carefully. Do that work first, and cutover day becomes boring, which is exactly what you want.