Not quite same situation but new user, install 3CX on a Pi a couple of months ago.
The "FINAL" was a surprise as no previous info.
Would be useful to build on the info provided by JohnS_3CX above in future Email alerts.
The Email (only) hints at having V18 means you do not need to take any action on the PBX itself.
Does not say explicitly that only change needed is on a firewall that can have FQDN entries (like expensive ones)
Does not mention the V18
build see Dashboard under Information/Version = 18.0 Update 2 (Build 314)
(as there is always logic in these update Emails then a flow chart would be really handy and show the questions and steps required to check as this flow of thoughts must be {even subconsciously} be in the mind of the person writing the Email? )
To check you update status on Dashboard hit the big blue icon bottom right.. "Updates"
Hopefully you will get...
Your system is up to date. Last checked: Today, 17:55
Automatically update 3CX
3CX will automatically check and download available and relevant updates on the selected date/time. Updates including 3CX supported firmwares for your existing IP Phones, language files, PUSH certificates and sip trunk templates will be applied automatically.
3CX "RELEASE" updates will also be downloaded and installed automatically. If the update is a "Alpha/Beta (unstable)" update, then this will not be automatically installed and must be installed manually if needed. Alpha/Beta updates are used to evaluate an upcoming version before it is officially released and should be used for testing and evaluation purposes. Do not install Alpha/Beta updates on your production systems.
When updates are applied, all 3CX Services will be restarted numerous times. So it is important that the checking for updates is done at a time when the pbx is in Out of office hours.
On Linux systems, this option also automatically installs Debian Security Updates.
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I like the PBX, I like the above too, it means with backups on (hope you have) {must look for a way to manually or automatically copy the completed backup to another disk somewhere i.e. off the Pi SD card } you don't have to do any normal updates and for those of us with a simple router/firewall no action needed.