Your scanner still emails PDFs, your backup scripts still send nightly reports, and none of them will ever learn OAuth 2.0: Email OAuth 2.0 Proxy learns it on their behalf. It listens on local IMAP, POP, and SMTP ports on your server, and when a client logs in the old-fashioned way with a username and password, the proxy swaps that exchange for a modern SASL XOAUTH2 token before the connection ever reaches the provider. The client never knows anything changed, so ancient mail apps, embedded devices, monitoring tools, and hand-rolled scripts keep sending and fetching mail through Outlook, Office 365, Gmail, Google Workspace, Fastmail, Yahoo, AOL, and any other provider that demands OAuth 2.0. The hop from your client to the proxy stays simple, while the proxy opens a fully encrypted TLS connection upstream, including STARTTLS negotiation for SMTP relays that require it. One proxy instance serves many accounts at once, with each mailbox mapped to its own local port and its tokens cached under a password you control. Optional plugins can even rewrite traffic in flight: strip Microsoft Defender Safe Links back to their real URLs, stop duplicate sent messages, or swallow test mail into a black hole. Setup is a single configuration file covering server ports, per-account scopes, and token endpoints, and the proxy then runs quietly as a headless service. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache-2.0 licensed.