I'm an experienced debian developer, and my company uses your Debian packages for Zabbix. There's a few concerns that needs to be addressed in your packages.
Upgrading from Zabbix 3.4 to 4.0 fails, because zabbix-sender contains files from zabbix-agent previous version, without declaring something like this:
Breaks: zabbix-agent (<= 1:4.0.22)
Replaces: zabbix-agent (<= 1:4.0.22)
Also, I find it a bit silly that the buster version is 1:4.0.22-1+buster and stretch is 1:4.0.22-1+stretch. Indeed, buster is lower than stretch in the alphabetical order. Can I suggest that you switch to:
so that the version from Stretch is always lower than then one in Buster and allows a correct upgrade?
Thomas Goirand (zigo)