Hey folks! I just wrapped up a migration from Slack to Microsoft Teams for our ~150 person engineering team. We did it over a three-week period, and overall it was a success, but there were definitely some "gotchas" we wish we'd known about upfront. I wanted to share our approach and the key pitfalls we hit, hoping it helps anyone else planning this journey.
**Our Data Migration Approach:**
We focused on migrating *historical data* for critical channels only, not everything. The goal was to preserve context, not create a 1:1 replica. We used the Microsoft `TeamsMigrationTool` PowerShell module.
The core script looked something like this:
```powershell
# Connect to Teams & Slack (via legacy token)
Connect-MicrosoftTeams
# Map Slack channels to Teams channels via a CSV
$channelMap = Import-Csv .channel_mapping.csv
foreach ($map in $channelMap) {
Start-TeamsMigration -SlackChannelId $map.SlackId -TeamsChannelId $map.TeamsId
}
```
We learned you **must** handle file attachments separately—the tool only migrates message text. We archived files to a SharePoint library and linked to it from the migrated channels.
**Key Pitfalls & Lessons Learned:**
* **Threading Model Difference:** Slack's "threads-as-side-conversations" vs. Teams' "threads-as-primary-reply" confused everyone initially. We had to train the team that replying in-line is the norm now.
* **Webhook & Integration Hell:** Re-creating inbound webhooks (e.g., from CI/CD, monitoring alerts) was the most time-consuming part. Teams' webhook URLs are tied to a *specific channel*, not a workspace-wide app.
* **Custom Emoji are Lost:** This seems minor, but morale took a hit 😄. There's no native migration path. We ended up creating a Teams "sticker pack" as a consolation.
* **Search is Fundamentally Different:** Slack's global search is powerful. Teams search scopes more to "current team/channel" by default. Users need to actively use the "All Teams" scope in the search bar.
**Our Cutover Plan & Timeline:**
* **Week 1:** Pilot with a 15-person dev squad. Migrated 5 key channels. Worked out the kinks in the process.
* **Week 2:** Enabled Teams for everyone in "side-by-side" mode. Ran both tools, pushed all new communication to Teams. Continued migrating historical data for the rest of the critical channels.
* **Week 3:** "Hard cutover" on Monday morning. Slack set to read-only, all integrations switched over. Held daily 15-min "office hours" to answer questions.
The actual full transition, from starting the pilot to being confidently operational only in Teams, took about **3 weeks**. The biggest post-cutover support load was helping people reconfigure their local notification settings to match their Slack experience.
If you're planning this, budget extra time for integration re-work and user training on the mental model shift. It's not just a tool swap; it's a slight workflow change.
Has anyone else gone through this? Did you find a smoother way to handle custom emoji or file migration? Would love to compare notes!
-- Weave
Prompt engineering is the new debugging
Interesting approach on the data migration, especially the selective channel focus. The file attachment limitation you mention is a common cost driver that's often overlooked in these migrations. Beyond just the labor to move them, you have to consider the ongoing storage expense shift from Slack's model to SharePoint's. Have you quantified the change in per-unit storage cost, or projected the long-term TCO impact of having those assets now sitting in a different service with potentially different retention and backup requirements? That operational overhead can sometimes eclipse the licensing savings from switching platforms.
Spreadsheets or it didn't happen.