Slack Messages Not Sending — What Causes It & How to Fix It

What Does This Error Mean?

Slack messages are spinning or failing to deliver — showing a warning icon or 'failed to send' notice. This is usually caused by a lost internet connection or a Slack service outage. A quick check of your connection and Slack's status page solves most cases.

Affected Models

Slack on Windows
Slack on Mac
Slack on iPhone
Slack on Android
Slack on browser

Common Causes

No internet connection or unstable network
Slack servers are experiencing an outage
Message is too long (over 40,000 characters)
The channel has been archived
You don't have permission to post in that channel

How to Fix It

Check your internet connection — open a webpage to confirm it's working.

Slack requires a live internet connection to send messages.
Go to status.slack.com to check for any active Slack outages.

If there's a known incident, you just need to wait for Slack to resolve it.
Check the message length — Slack has a 40,000 character limit per message.

If your message is very long, split it into multiple shorter messages.
Check if the channel is archived — archived channels are read-only.

Look for an 'Archived' label at the top of the channel. Ask an admin to unarchive it if needed.
Restart the Slack app, and ask a workspace admin if you have posting permission.

Some channels are restricted to certain members or roles.

When to Call a Professional

This is a connectivity or permissions issue. No technician is needed — check Slack's status page and your network first.

Frequently Asked Questions

What does the warning triangle mean on a Slack message?

A warning triangle next to a message means Slack failed to deliver it. Click the triangle to see options — you can retry sending or delete the message. This usually happens during a connection drop or brief outage.

Is there a message length limit in Slack?

Yes — Slack messages have a limit of 40,000 characters. This is equivalent to roughly 6,000–8,000 words. For very long content, use a Slack document (Post) or share a file instead.

Can I retry a failed Slack message?

Yes — click the warning triangle icon next to the failed message. You'll see an option to 'Try Again' which resends the message. If retrying keeps failing, check your internet connection first.