Local-first
The administrator controls the system that receives local SMTP and holds queued mail.
About the project
A focused answer to
a real compatibility problem.
RelayBridge is an independent open-source project for administrators who need working legacy devices to coexist with modern mail platforms, starting with Microsoft 365.
01 / WHY
Keep useful equipment useful.
Printers, scanners, appliances, and line-of-business systems often have a longer operational life than the authentication methods they were built around.
RelayBridge is designed to close that gap without asking every device to understand OAuth and without introducing a RelayBridge-operated cloud relay into the mail path.
02 / PRINCIPLES
Inspectability
Architecture, limitations, and source should be available for direct scrutiny.
Precision
Claims should match real protocol boundaries, especially around authorization and delivery.
03 / STATUS
Built in the open,
before calling it ready.
RelayBridge application source is public under the Mozilla Public License 2.0. Its first public Windows release candidate, v1.0.0-rc.1, is available as an unsigned pre-release for evaluation and community testing. A signed stable release and the final support matrix are not yet available.
RelayBridge was created and is primarily maintained by @yuvaraj-builds-ai.
04 / FUTURE
Future direction
Microsoft 365 is the first supported provider. RelayBridge is architected with potential future provider expansion in mind.
Google Workspace and other modern mail providers may be evaluated later. Future integrations will only be added when they meet RelayBridge's existing local-first, security, durability, and reliability standards.
Public release candidate
Review RelayBridge v1.0.0-rc.1.
Understand the unsigned pre-release boundary, verify the installer hash, and inspect the public MPL-2.0 source.