A new Pr for this suggest will soon be submited (from ddurieux) for integration in 9.2.

Currently in progress:

https://github.com/glpi-project/glpi/pull/2240

Will certainly be in 9.2

tarted with the native notification feature:

https://github.com/glpi-project/glpi/pull/2207

This will be present in 9.2 release

PR merged.