Recently there is one particular domain complaining that they can't sent out email intermittently and often receiving error "421 too many concurrent smtp connections" . When checking in the exim_mainlog, I found that their IP address always exceeding the allowed concurrently SMTP connection limit which is 100.
My question is how can I find out which user of the domain is causing the problem?
My question is how can I find out which user of the domain is causing the problem?