What factors determine inbox vs spam?

The inbox versus spam decision weighs multiple factors:

Sender reputation: Your historical track record at IP and domain level.

Authentication: Whether SPF, DKIM, and DMARC pass and align.

Engagement signals: How recipients have interacted with your previous messages.

Complaint rates: How often recipients mark your mail as spam.

Content analysis: Spam patterns, suspicious URLs, known bad signatures.

User-level history: Has this specific recipient engaged with you before?

These factors combine through machine learning models. No single factor guarantees inbox or spam.

The harbor master weighs your papers, your cargo, your history, and your crew's behavior before assigning you a berth.