Mail from a club sent by a list mailer (ezmlm) to one of our sub-accounts bounce with the error message "421 Too many concurrent SMTP connections from this IP address". The IP address listed is 22.214.171.124
I'd say ask the club to see if ezmlm can limit the number of simultaneous connections it makes to a given SMTP server. It appears that exmlm usually is paired with qmail for sending, qmail has a parameter called concurrencyremote which can limit the number of simultaneous total sends (not just to one server, but total). Reducing this total value will effectively also limit the number going to one server.
Some guides tell you to raise this parameter to increase performance without telling you what it does or the drawbacks. It seems that the apparent out-of-the-box value would be 20, which I would have thought to be fine.
*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.