We are making good progress building a mail server. The server is a KVM running CentOs 8.2 with vcpus=2 and ram=4GB. The system is under heavy load and is likely limited by disk performance. The load is generated by a second KVM using SMTP to send email. Everything seems to be working except there is nothing in /var/log/maillog for a period of 3 minutes. I'm not sure what is causing the omission of logs and how to correct this issue.
I'm concerned that we are not following this recommendation, "Don't overwhelm the disk with mail submissions. Optimize the mail submission rate by tuning the number of parallel submissions and/or by tuning the Postfix in_flow_delay parameter setting." There is no indication in /var/log/maillog of problems (other than 3 minutes of missing logs). I do not know if "overwhelming the disk" would lead to shutting down data going to the maillog altogether. I will set in_flow_delay = 2s for this KVM mail server this evening. The performance snapshots below seem to show: cpu load average is not heavy, plenty of ram free, no swapping (stable at 108Mi), dm-0 is working hard at 129 tps and postfix seems to be keeping up with the load with 39-50 emails in the queue. This run started at 03:05 and created two minutes of data in /var/log/maillog -- and then nothing for 3 minutes starting at 03:07. I am certain the email in the missing three minutes was actually delivered or I would be seeing lots of negative feedback from our subscribers. >>>>> 03:07:04 up 17:31, 0 users, load average: 0.42, 0.26, 0.10 total used free shared buff/cache available Mem: 3.7Gi 832Mi 2.0Gi 101Mi 931Mi 2.5Gi Swap: 1.0Gi 108Mi 915Mi Device tps kB_read/s kB_wrtn/s kB_read kB_wrtn dm-0 129.00 0.00 2373.50 0 4747 incoming/active queue: T 5 10 20 40 80 160 320 640 1280 1280+ TOTAL 39 39 0 0 0 0 0 0 0 0 0 gmail.com 8 8 0 0 0 0 0 0 0 0 0 att.net 7 7 0 0 0 0 0 0 0 0 0 bellsouth.net 7 7 0 0 0 0 0 0 0 0 0 sbcglobal.net 7 7 0 0 0 0 0 0 0 0 0 aol.com 4 4 0 0 0 0 0 0 0 0 0 icloud.com 4 4 0 0 0 0 0 0 0 0 0 yahoo.com 1 1 0 0 0 0 0 0 0 0 0 outlook.com 1 1 0 0 0 0 0 0 0 0 0 deferred queue: T 5 10 20 40 80 160 320 640 1280 1280+ TOTAL 1 0 0 0 0 0 0 0 0 0 1 icloud.com 1 0 0 0 0 0 0 0 0 0 1 >>>>> 03:07:11 up 17:31, 0 users, load average: 0.36, 0.25, 0.10 total used free shared buff/cache available Mem: 3.7Gi 858Mi 1.9Gi 101Mi 933Mi 2.5Gi Swap: 1.0Gi 108Mi 915Mi Device tps kB_read/s kB_wrtn/s kB_read kB_wrtn dm-0 121.50 0.00 2326.00 0 4652 incoming/active queue: T 5 10 20 40 80 160 320 640 1280 1280+ TOTAL 56 56 0 0 0 0 0 0 0 0 0 gmail.com 13 13 0 0 0 0 0 0 0 0 0 att.net 11 11 0 0 0 0 0 0 0 0 0 sbcglobal.net 11 11 0 0 0 0 0 0 0 0 0 bellsouth.net 9 9 0 0 0 0 0 0 0 0 0 icloud.com 6 6 0 0 0 0 0 0 0 0 0 yahoo.com 5 5 0 0 0 0 0 0 0 0 0 rocketmail.com 1 1 0 0 0 0 0 0 0 0 0 deferred queue: T 5 10 20 40 80 160 320 640 1280 1280+ TOTAL 1 0 0 0 0 0 0 0 0 0 1 icloud.com 1 0 0 0 0 0 0 0 0 0 1 Thanks, Greg