What is a sending node or data center?

A sending node or data center is a location containing email sending infrastructure: servers, network equipment, IP addresses, and supporting systems.

What's in a sending node:

MTA servers: The machines that actually send email

Queue servers: Holding pending messages for delivery

Network infrastructure: Routers, switches, bandwidth

IP address blocks: The addresses used for sending

Storage: Logs, queued messages, local caches

Why multiple locations:

Reduced latency: Sending from Europe to European mailbox providers is faster than from the US

Redundancy: If one data center fails, others continue operating

Capacity distribution: Spread load across locations

Data residency: Some regulations require data processing in specific regions

IP diversity: Different IP ranges from different network providers

Large ESPs operate nodes across North America, Europe, Asia Pacific, and sometimes South America. Traffic routes to appropriate nodes based on destination, load, and health.

When an ESP mentions "global infrastructure," they're referring to this distributed network of sending nodes working together as a unified platform.