Call it the Work At Home Button.
It is a feature that turns of email Sync in Outlook. Imagine that you are working late but you would not like to send the emails right away. This might be becasue you dont want replies or that Your customers feel pressured to answer Your mails when you work late.
For whatever reason, here is how you disable Outlook Sync in two Clicks
The Language here is Norwegian, but button location and iconography is similar in any other language
I found this feature troubleshooting an Outlook that said “working offline” and the user did not realize what had happened.