Spam folder
Where messages flagged as junk land — the worst inbox placement outcome short of outright rejection.
The spam folder (or junk folder) is the inbox location where mail flagged as unwanted is quarantined. Recipients rarely check spam folders; mail that lands there has effectively been blocked from their attention. Spam-folder placement is the worst inbox outcome short of outright rejection.
Mail lands in spam for many reasons: low sender reputation, failed authentication, content patterns that trip spam filters (excessive caps, link-heavy bodies, image-only messages, common spam-trigger phrases), or personal user action (the recipient previously marked similar messages as spam). The signals are layered and provider-specific.
Once a sender lands in spam consistently with a given recipient, recovery is hard. Engagement re-builds reputation, but engagement requires the recipient to actually see the messages. The structural fixes are at the sender level: clean authentication, list hygiene, engagement-focused content, and patience as reputation rebuilds. Quick fixes — switching IPs, changing From: addresses — rarely work and sometimes worsen the problem.