I am a freshman,and I first use the exim4.89 on ubuntu 16.04,I found this problem ,the log show that:
3900 SMTP>> 421 Too many concurrent SMTP connections; please try again later.
3900 LOG: connection_reject MAIN
3900 Connection from [**********] refused: too many connections
3900 Listening...
,so where can I set the max connection number ,I didn't see any useful options in /usr/exim/configure file,thank you very much
Exim's smtp_accept_max-* options are for controlling concurrent connections number. This parameters force each submitter to limit number of created sessions to some reasonable value. In other word that error occur not because of server misconfiguration but rather because of misconfiguration on the other side. I suppose it is some kind of mailgun that toss the messages at some insane rate.