Restriction to GEO location

[brunt82]

Unfortunately, we had to deactivate the app today because too many false positive emails were delivered.

The following use case does not seem to have been considered: If a user is in a public WiFi network of a chain store, the user does not necessarily go online with an IP address of the store/the current location. Instead, it can also be an IP address of the headquarters. This leads to confusion because the users are said to have accessed the app from 600 km away.

In conjunction with calendar use, a mobile device in the "wrong" WiFi network can quickly lead to misleading emails.

Therefore, my suggestion would be to introduce a whitelist not for individual IP addresses (#659) but for geo-locations. See https://www.maxmind.com/en/geoip-databases.
If the IP address is not in an allowed country (e.g. Germany), an email should be sent.