continous querry from Microsoft Datacenter ip-adressen to microsoft-server-activesync

Can someone explain the following.

We have a hybrid exchange 2016 configuration.

We see on our Web Application firewall continuous logs from connecting to out activesync  webservice from microsoft Datacenters ip's over Europe. Users are mentioned who have outlook on there Iphone and the mailbox is onpemise.

The querry string is cmd=ping&User=<domainname>%5C<username>$DeviceID=<DeviceID>&Devicetype=outlook

Can someone explain this to me