What is a sending pipeline?

A sending pipeline is the complete workflow an email traverses from campaign creation to inbox delivery. It encompasses list selection, suppression filtering, content rendering, personalization, queue management, SMTP transmission, bounce processing, and event tracking. Think of it as an assembly line—each station performs a specific function, and the email moves through sequentially.

Modern ESP pipelines handle millions of emails hourly. Key stages include: validation (checking addresses against suppression lists), rendering (generating personalized HTML/text versions), signing (applying DKIM signatures), queuing (organizing for optimal delivery), transmission (SMTP handoff), and tracking (logging opens, clicks, bounces). Each stage has potential failure points.

Pipeline visibility separates sophisticated senders from novices. Understanding your pipeline helps diagnose issues: Are emails stuck in queue? Failing at SMTP negotiation? Being rendered incorrectly? Enterprise ESPs provide pipeline monitoring dashboards. Smaller senders rely on support, but knowing these stages exist helps you ask better questions when things go wrong. Review My Emails can help identify where your specific messages might be encountering friction.