The removal of a letter from the mail server from the phone is displayed in the logs as a connection from an external IP owned by Microsoft

There is: a corporate Kerio mail server, Outlook / Mail.ru email clients on the phone (Android / IOS). When deleting or moving a letter in the server logs, the following records are observed:

[28 / Jun / 2018 15:51:07] {DELETE} Protocol: IMAP, User: name.surname@mydomain.ru, IP: 94.100.185.209, Folder: ~name.surname@mydomain.ru/INBOX, From: "User Shmuzer", Subject: "sub"

The question is, why is it removed or moved from outside, from IP 94.100.185.209 (for mail.ru client), for Outlook, respectively, from IP owned by Microsoft? Is this a feature of the IMAP protocol?

Tested on a decent amount of devices and letters.