2:24 AM PST
Thank you for your patience. We identified the culprit and reverted a recent change that caused this behavior. Affected users should now be able to post messages. Please reload Slack using Command + Shift + R (Mac) or Ctrl + Shift + R (Windows/Linux), and let us know if you need additional help.
2:35 PM PST
Some users are experiencing issues posting messages and are seeing the error message "Slack couldn’t send this message". We're investigating and will post an update as soon as possible.
1:36 PM PST