How does an email travel through the ecosystem?

An email's journey starts when you hit send. Your ESP queues the message, signs it with DKIM, and transmits via SMTP to the recipient's mailbox provider. The message travels through multiple servers, each adding headers documenting its path.

The receiving MBP performs extensive checks: DNS lookups verify SPF authorization and DKIM signatures, DMARC policy determines enforcement, blocklist queries check sender reputation, spam filters analyze content, and engagement history influences scoring. This happens in milliseconds.

Based on these checks, the MBP delivers to inbox, spam, or rejects entirely. The decision gets logged and affects future reputation. Bounces return to your ESP. The recipient's engagement (opens, clicks, complaints) feeds back into reputation systems, completing the cycle that influences your next send.