What causes "Slack Messages Not Sending"?

Slack-wide incident (Feb 26-27, 2025 outage left messages failing to send) Unstable network, VPN or proxy Firewall blocking Slack connections Corrupted cache For bots/integrations: the app isn't a member of the channel

How do I fix "Slack Messages Not Sending"?

1. Check for an outage: Open slack-status.com During an incident, wait; Slack queued undelivered messages for resend after the Feb 2025 outage 2. Retry and restart: Click the failed message and choose to retry Fully quit Slack (or close the browser) and reopen On mobile, swipe the app away and reopen 3. Clear the cache: Desktop: Help > Troubleshooting > Clear Cache and Restart Web: clear your browser cache and reload 4. Fix network issues: Disconnect VPN/proxy temporarily Switch to a wired or different network Run slack.com/help/test and share errors with IT 5. Fix bot posting failures: Invite the app to the channel with /invite @AppName For private channels, a channel member must add the app

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Slack Messages Not Sending

Workaround available Mac, Windows, Web, iOS, Android Updated October 21, 2026

Quick answer

Messages stuck with a 'not sent' warning are usually a connection problem on your side or a Slack outage. Check slack-status.com, then clear the cache, restart Slack and test without VPN/proxy.

Most likely fix: Check for an outage.

Symptoms

Messages show a red warning or 'Couldn't send this message', stay greyed out, or send only after retrying.

Why it happens

Slack-wide incident (Feb 26-27, 2025 outage left messages failing to send)
Unstable network, VPN or proxy
Firewall blocking Slack connections
Corrupted cache
For bots/integrations: the app isn't a member of the channel

How to fix it

Try these in order — the most common fix is first.

1. Check for an outage
1. Open slack-status.com
2. During an incident, wait; Slack queued undelivered messages for resend after the Feb 2025 outage
2. Retry and restart
1. Click the failed message and choose to retry
2. Fully quit Slack (or close the browser) and reopen
3. On mobile, swipe the app away and reopen
3. Clear the cache
1. Desktop: Help > Troubleshooting > Clear Cache and Restart
2. Web: clear your browser cache and reload
4. Fix network issues
1. Disconnect VPN/proxy temporarily
2. Switch to a wired or different network
3. Run slack.com/help/test and share errors with IT
5. Fix bot posting failures
1. Invite the app to the channel with /invite @AppName
2. For private channels, a channel member must add the app

This guide also covers

slack messages not sending
slack couldn't send this message
slack message failed to send
slack not sending messages

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