Malware
MAILCREEP
According to Zscaler, MAILCREEP is a Golang-based backdoor leveraging the Microsoft Graph API for its C2 communications.
MAILCREEP is a Windows malware family.
Background
Zscaler describes MAILCREEP as a backdoor written in Golang that routes its command-and-control traffic through the Microsoft Graph API.
Source: Malpedia (Fraunhofer FKIE).