Hi, thanks for responding.
By the way I'm sorry, I just remembered from your response that the messagelabs logs are older and might be linked to a prior error we encountered - the "Too many connections" error. The network was fine, SME server was simply not accepting more connections. We did increase the limit from the default 10 to 40. That's when this new error shows up.
I'll try to get the latest messagelabs logs for this exact problem and post it again.
We do monitor the network / Internet connection, and there was no discernible downtime at any time.
As for the VM we did suspect it at first, so we checked the network, CPU, memory, disk. Only thing a bit high is disk latency which can reach 70ms and up to 300ms at its peak, though most of the time it's around 10-20ms. We did increase the disk share / priority to see if errors would go away, but didn't.
Resources: VM is on VMWare esxi 6.7, HP proliant host,
SME server has 4GB allocated memory, 250GB disk, 1 vCPU.
We can see ~75% memory use most of the time. CPU use usually really low.
The guest shares the host with 2 other VMs (less busy web servers).
We use SME server solely for email with email clients, <200 users, with ~1% using webmail.
As for network traffic,
The peak traffic is around 200 emails in an hour, counting internal emails.
External traffic bandwidth total is around 0.5GB per day.
Given error distributed at all hours, and not just during peak hours.
Thanks for the suggestion, we'll try adjusting the VM resources (CPU, memory) upwards and see if there's any improvement.
Just found this, will read up on this:
https://wiki.contribs.org/Virtual_SME_ServerAs for the SME Server config, here it is.
==================
Base configuration
==================
SME server version: 9.2
SME server mode: serveronly
Running Kernel: 2.6.32-754.31.1.el6.x86_64
===========================
New RPMs not in base system
===========================
Loaded plugins: fastestmirror, post-transaction-actions, smeserver
Loading mirror speeds from cached hostfile
* base: ftp.cuhk.edu.hk
* smeaddons: mirrors.mab974.re
* smeos: mirrors.mab974.re
* smeupdates: mirrors.mab974.re
* updates: mirror-hk.koddos.net
Extra Packages
lshw.x86_64 2.17-1.el6.rf @smecontribs
perl-Config-IniFiles.noarch 2.72-2.el6 @smecontribs
perl-Filesys-DiskFree.noarch 0.06-1.2.el6.rf @smecontribs
perl-Proc-ProcessTable.x86_64 0.48-1.el6 @smecontribs
smeserver-affa.noarch 3.2.2.3-8.el6.sme @smecontribs
smeserver-crontab_manager.noarch 2.4-3.el6.sme @smecontribs
smeserver-diskusage.noarch 0.2.0-2.el6.sme @smecontribs
smeserver-hwinfo.noarch 1.2-2.el6.sme @smecontribs
smeserver-mailstats.noarch 1.1-11.el6.sme @smecontribs
smeserver-qmHandle.noarch 1.4-12.el6.sme @smecontribs
smeserver-userpanel.noarch 1.2-3.el6.sme @smecontribs
smeserver-userpanels.noarch 1.1-5.el6.sme @smecontribs
smeserver-vacation.noarch 1.1-26.el6.sme @smecontribs
smeserver-wbl.noarch 0.3.0-19.el6.sme @smecontribs
===========================
Custom and modified templates
===========================
/etc/e-smith/templates-custom/var/service/qpsmtpd/config/relayclients/10CustomAllowRelay: MANUALLY_ADDED, ADDITION
/etc/e-smith/templates-custom/home/e-smith/ssl.crt: MANUALLY_ADDED, OVERRIDE
===========================
Modified events
===========================
/etc/e-smith/events/email-update/templates2expand/var/qmail/control/badmailfrom: MULTIPLE_RPM_OWNERS smeserver-qpsmtpd-2.4.0-39.el6.sme, smeserver-wbl-0.3.0-19.el6.sme
/etc/e-smith/events/email-update/templates2expand/var/service/qpsmtpd/config/badhelo: MULTIPLE_RPM_OWNERS smeserver-qpsmtpd-2.4.0-39.el6.sme, smeserver-wbl-0.3.0-19.el6.sme
=======================
Additional repositories
=======================
base: enabled
centosplus: disabled
contrib: disabled
extras: disabled
fasttrack: disabled
smeaddons: enabled
smecontribs: disabled
smedev: disabled
smeextras: enabled
smeos: enabled
smetest: disabled
smeupdates: enabled
smeupdates-testing: disabled
updates: enabled