since around the time Interworx 4.0 has been released we are struggling with SMTP availability issues on our server - SMTP service becomes unavailable - you can connect but the server never responds.
I found out that this happens because the number of qmail-smtpd processes running reaches the value specified in /var/qmail/control/concurrencyincoming.
Unfortunately, increasing this value does not help, because some qmail-smtpd processes seem to just never end. So the only effect is that it takes longer time to fill all the free “slots”.
As a temporary solution, I regularly kill all qmail-smtpd processes which are running for more than an hour, but that is just a workaround, and I would really like to find proper permanent solution.
How can it be that some qmail-smtpd processes run for hours or even days/weeks? Shouldn’t they timeout? I have not customized any timeouts and the only non-default timeout seems to be /var/qmail/control/timeoutremote which is probably preset by interworx and is set to 600.
It can be just coincidence, but is it possible that some changes in Interworx 4.0 could cause this? It seems to happen from around the time Iworx 4.0 version has been released. Should I open a support ticket?
Thanks very much for help.