imho. * don't reboot a server until its really necessary - like a kernel upgrade etc. rebooting is never a solution, this is just pointless "panic mode": if

imho. * don't reboot a server until its really necessary - like a kernel upgrade etc. rebooting is never a solution, this is just pointless "panic mode": if its still possible: investigate why the system becomes slowed down ... a hardware-problem/ram or other resource-constaints or "real" dos-problems like out-of-tcp-connections etc. * for this: use proper monitoring - mainly graphing - as simple as munin or more complex like prometheus & grafana hey ... its just a small mailsystem you don't need any of the latest and greatest paid service for this. * personally i operate a small mailsystem since the ancient times of the internet - aka 90ties - sendmail/qmail/qmail-ldap and atm exim-ldap. around 300 mailboxes - more or less my friends & familly. for example: i'm using dynamic blocking similar to fail2ban for smtp-auth brute-force - implemented in bash/python; spamassassin & clamav for spam - custom config: mainly blocked most of the "crap" TLDs like .icu etc...