“Spectrum limits the number of concurrent connections from a sender, as well as the total number of connections allowed. Limits vary based on the reputation of the IP address. Reduce your number of connections and try again later.”
How to I limit the number of concurrent connections?
You don’t say who ‘Spectrum’ is. One way is to limit the number of connections to a mail server is to slow down your sending. Look for the ‘throttle’ settings in your phpList config.php file, and increase the number of seconds between emails.