Email Deliverability

The ability of an email to reach the recipient's inbox rather than being blocked, bounced, or filtered to spam. Deliverability depends on sender reputation (IP and domain), authentication (SPF, DKIM, DMARC), content quality, list hygiene, and engagement metrics. SMTP status codes like 250 (OK), 421 (try again), and 550 (rejected) directly reflect deliverability outcomes at the protocol level.