The last 2-3 days there was a significant slow down with message sending, sometimes 15 seconds, via the default #chatmail relay .... Wasn't a CPU/RAM or other resource problem but a software configuration / implementation problem. After some hours of debugging it was solved by providing the "speed-adjust" proxy option to #postfix. message sending should be back to sub-second. No message was lost. Lesson learned: just search for "speed" in postfix docs first (and fix the offending module later).