Fetchmail Adapter for Exchange Online / Graph API

Challenge

After migrating to Exchange Online, an existing business application still required a Fetchmail-compatible interface and could not be modified.

Approach

I built a Go-based drop-in replacement for Fetchmail with OAuth2 and Graph API integration. The tool reproduces expected Fetchmail behavior, adds robust retry and logging, and implements secure token/TLS handling.

Snapshot

• Industry: Industrial enterprise
• Time frame: 2024
• Technologies
  • Go (custom implementation)
  • Microsoft Graph API
  • OAuth2 / TLS
  • Exchange Online

The solution kept the commercial legacy software running unchanged and established a stable bridge to modern cloud mail infrastructure.