What are the possible placement folders (inbox, spam, promotions, updates, etc.)?

Modern mailbox providers sort messages into multiple destinations:

Primary Inbox: The main folder users check regularly. The goal for most senders.

Spam/Junk: Messages flagged as unwanted. Rarely checked. Effectively invisible.

Promotions (Gmail): Marketing and commercial messages. Still inbox, just categorized.

Social (Gmail): Notifications from social networks.

Updates (Gmail): Receipts, confirmations, transactional messages.

Focused/Other (Outlook): Microsoft's two-tier inbox system.

The Promotions tab is still the inbox. Only spam folder represents true placement failure. Users can and do engage with tabbed categories.