PingMail
An SMTP to webhook bridge that replaces on-premises relays
Overview
PingMail replaces the Windows SMTP relay that tends to sit forgotten in the corner of a client network, without asking the devices that depend on it to change.
The problem
Printers, backup appliances, and line-of-business applications still send mail over port 25 with no authentication. The usual answer is an internal relay: another VM to patch, no useful audit trail, and an open relay waiting to happen if the scoping is wrong.
How it works
A Go daemon listens on the internal network, checks the sender envelope, and forwards the message over HTTPS to a Cloudflare Worker. The Worker verifies the bearer token, writes delivery metadata to D1, and hands the message to a transactional mail API. Nothing inbound needs to be exposed.
Design decisions
- The agent has no runtime dependencies and queues locally when the link is down.
- Requests carry an HMAC signature, so the Worker rejects anything it did not issue a token for.
- Each customer has separate tokens and D1 rows, which also gives per-customer delivery history.
- The admin interface is rendered by the same Worker, so there is no second thing to host.