Junk folder
Microsoft's term for spam folder — Outlook routes filtered mail there.
The junk folder is Microsoft's name for the spam folder in Outlook, Outlook.com, and Hotmail. Functionally equivalent to Gmail's Spam folder, the junk folder is where Microsoft's filtering routes mail it suspects of being unsolicited, fraudulent, or malicious. Users can mark messages as "not junk" (analogous to "not spam") to retrain the classifier.
Microsoft's filtering uses different signals than Google's. Microsoft weights authentication very heavily — failing SPF or DKIM is nearly a guarantee of junk placement. Microsoft also uses Smart Network Data Services (SNDS) which gives senders visibility into their reputation as seen by Microsoft's filters. SNDS data is one of the few first-party deliverability signals receivers actually publish.
For senders, the practical implication is that Outlook deliverability requires separate optimization from Gmail. An email that lands in Gmail Primary may land in Outlook junk if SPF/DKIM aren't properly aligned. Test against both. Our inbox-preview surface renders the same email as it appears in both Outlook desktop and Gmail web so you can compare layout.