What is connection concurrency?

Connection concurrency refers to how many simultaneous **SMTP** connections an **MTA** maintains to receiving servers. Higher concurrency means faster delivery but risks overwhelming receivers or triggering rate limits.

MBPs impose limits on concurrent connections from any single sender. Exceeding limits causes connection rejections and potential reputation damage. MTAs must balance delivery speed against provider tolerances, adapting concurrency per destination.

Optimal concurrency depends on: your volume, receiving server policies, your reputation level, and time sensitivity. High-reputation senders can maintain more connections. New or recovering senders should use conservative settings. Most ESPs manage this automatically based on their infrastructure knowledge.