Hi, I am a Senior Network Engineer at one of the biggest ISP's in Moldova. I have about 8 experience of experience in networking, and especially I have experience with Cisco and Juniper routers and switches. We are using Zabbix as a monitoring system with more then then 2500 hosts in zabbix, with about 600.000 of items, and with 4 proxies. For this enviroment we have email and Slack notifications, we also have tried different other types of notifications, WhatsUP/telegram/SMS and others notification so I already dealt with this before.
I can help you with your task as I already dealt with this before.