Outlook users may not be able to send emails at the moment. The behavior is caused by a bug that affects classic Outlook. Specifically, you may see the issue after updating classic Outlook to Version 2412 (Build 18324.20168). Microsoft has a fix for the issue on the way and you can also mitigate the problem by rolling back classic Outlook to a previous version.
The new Outlook is unaffected by the issue, so only those on classic Outlook may run into problems.
