Hello, We use a Postfix installation on Debian 9 in our network to serve as a send-only SMTP server for a very large application in our school district. This application does not have its own built-in SMTP server and requires a relay to send notification e-mails to students, teachers, and parents topping out at around 10,000 e-mails per day. Our hosted e-mail solution (G Suite) has a sending cap that we hit with this application so we setup this Postfix installation to serve as an alternative.
However, whenever Postfix gets a large e-mail load it processes the e-mails for around 30-45 minutes and then consistently uses around 70-80% of the CPU effectively locking up the entire system so much so that I can't even login and debug without either disabling the network card in VMWare or rebooting the system totally. The VM has 2 CPU cores and 4GB RAM allocated to it which I thought was plenty for this application. I see no errors or alarms in the mail log nor syslog. The only odd message I see is a series of ^@ symbols before the system freezes: Jan 15 00:42:41 mailrelay opendkim[1643]: 385B38094E: DKIM-Signature field added (s=mailrelay, d=oconee.k12.sc.us) Jan 15 00:42:41 mailrelay postfix/qmgr[5601]: 385B38094E: from=< aaaaaaaa...@oconee.k12.sc.us>, size=2282, nrcpt=1 (queue active) Jan 15 00:42:41 mailrelay postfix/smtpd[6128]: 8BFCC80968: client=unknown[DDD.DD.DD.DD], sasl_method=LOGIN, sasl_username=AAAAAAAAAAA@ oconee.k12.sc.us Jan 15 00:42:41 mailrelay postfix/cleanup[6375]: 8BFCC80968: message-id=< 734906173.4337.1515994961560.javamail.aaaaaaaa...@oconee.k12.sc.us> Jan 15 00:42:41 mailrelay opendkim[1643]: 8BFCC80968: DKIM-Signature field added (s=mailrelay, d=oconee.k12.sc.us) Jan 15 00:42:41 mailrelay postfix/qmgr[5601]: 8BFCC80968: from=< aaaaaaaa...@oconee.k12.sc.us>, size=2370, nrcpt=1 (queue active) Jan 15 00:42:41 mailrelay postfix/smtpd[6128]: B66B38096E: client=unknown[DDD.DD.DD.DD], sasl_method=LOGIN, sasl_username=AAAAAAAAAAA@ oconee.k12.sc.us Jan 15 00:42:41 mailrelay postfix/cleanup[6375]: B66B38096E: message-id=< 902964141.4338.1515994961733.javamail.aaaaaaaa...@oconee.k12.sc.us> Jan 15 00:42:41 mailrelay opendkim[1643]: B66B38096E: DKIM-Signature field added (s=mailrelay, d=oconee.k12.sc.us) Jan 15 00:42:41 mailrelay postfix/qmgr[5601]: B66B38096E: from=< aaaaaaaa...@oconee.k12.sc.us>, size=3705, nrcpt=1 (queue active) Jan 15 00:42:41 mailrelay postfix/smtpd[6128]: E39EA8096F: client=unknown[DDD.DD.DD.DD], sasl_method=LOGIN, sasl_username=AAAAAAAAAAA@ oconee.k12.sc.us Jan 15 00:42:41 mailrelay postfix/cleanup[6375]: E39EA8096F: message-id=< 1233892182.4339.1515994961918.javamail.aaaaaaaa...@oconee.k12.sc.us> Jan 15 00:42:41 mailrelay opendkim[1643]: E39EA8096F: DKIM-Signature field added (s=mailrelay, d=oconee.k12.sc.us) Jan 15 00:42:42 mailrelay postfix/qmgr[5601]: E39EA8096F: from=< aaaaaaaa...@oconee.k12.sc.us>, size=2281, nrcpt=1 (queue active) Jan 15 00:42:42 mailrelay postfix/smtpd[6128]: 25EFC80970: client=unknown[DDD.DD.DD.DD], sasl_method=LOGIN, sasl_username=AAAAAAAAAAA@ oconee.k12.sc.us Jan 15 00:42:42 mailrelay postfix/cleanup[6375]: 25EFC80970: message-id=< 2097536797.4340.1515994962141.javamail.aaaaaaaa...@oconee.k12.sc.us> Jan 15 00:42:42 mailrelay opendkim[1643]: 25EFC80970: DKIM-Signature field added (s=mailrelay, d=oconee.k12.sc.us) Jan 15 00:42:42 mailrelay postfix/qmgr[5601]: 25EFC80970: from=< aaaaaaaa...@oconee.k12.sc.us>, size=2486, nrcpt=1 (queue active) Jan 15 00:42:42 mailrelay postfix/smtpd[6128]: 5329380972: client=unknown[DDD.DD.DD.DD], sasl_method=LOGIN, sasl_username=AAAAAAAAAAA@ oconee.k12.sc.us Jan 15 00:42:42 mailrelay postfix/cleanup[6375]: 5329380972: message-id=< 951323567.4341.1515994962327.javamail.aaaaaaaa...@oconee.k12.sc.us> Jan 15 00:42:42 mailrelay opendkim[1643]: 5329380972: DKIM-Signature field added (s=mailrelay, d=oconee.k12.sc.us) Jan 15 00:42:42 mailrelay postfix/qmgr[5601]: 5329380972: from=< aaaaaaaa...@oconee.k12.sc.us>, size=2326, nrcpt=1 (queue active) Jan 15 00:42:42 mailrelay postfix/smtpd[6128]: 8EF0980973: client=unknown[DDD.DD.DD.DD], sasl_method=LOGIN, sasl_username=AAAAAAAAAAA@ oconee.k12.sc.us Jan 15 00:42:42 mailrelay postfix/cleanup[6375]: 8EF0980973: message-id=< 484411487.4342.1515994962572.javamail.aaaaaaaa...@oconee.k12.sc.us> Jan 15 00:42:42 mailrelay opendkim[1643]: 8EF0980973: DKIM-Signature field added (s=mailrelay, d=oconee.k12.sc.us) Jan 15 00:42:42 mailrelay postfix/qmgr[5601]: 8EF0980973: from=< aaaaaaaa...@oconee.k12.sc.us>, size=2408, nrcpt=1 (queue active)^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^ @^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^ @^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^ @^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^ @^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^ @^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^ @^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^ @^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@ Jan 15 09:31:40 mailrelay opendkim[668]: OpenDKIM Filter v2.11.0 starting (args: -x /etc/opendkim.conf) Jan 15 09:31:43 mailrelay postfix/postfix-script[849]: starting the Postfix mail system Jan 15 09:31:43 mailrelay postfix/master[851]: daemon started -- version 3.1.6, configuration /etc/postfix Jan 15 09:31:43 mailrelay postfix/qmgr[853]: 2753880968: from=< aaaaaaaa...@oconee.k12.sc.us>, size=5027, nrcpt=1 (queue active) Jan 15 09:31:43 mailrelay postfix/qmgr[853]: 989CD80966: from=< aaaaaaaa...@oconee.k12.sc.us>, size=2176, nrcpt=2 (queue active) Jan 15 09:31:43 mailrelay postfix/qmgr[853]: DDEC880970: from=< aaaaaaaa...@oconee.k12.sc.us>, size=2229, nrcpt=1 (queue active) After a reboot usually Postfix finishes its mails and continues like nothing ever happened. I am at a loss how to debug or tweak any further. Do I need to implement some type of load-balancing? Is there a way I can debug more during the time of the freeze? I have also tried re-installing Debian with a fresh ISO (I compared MD5 hashes) and fresh install of Postfix/OpenDKIM. (copied config files) Thanks for your help -- This message may contain confidential information and is intended only for the individuals named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately by e-mail if you have received this e-mail by mistake and delete this e-mail from your system. If you are not the intended recipient you are notified that disclosing, copying, distributing or taking any action in reliance on the contents of this information is strictly prohibited.
