truemail-go

Stop sending to dead emails. Clean your list before every campaign.

Every bad address on your list costs you: it bounces, it drags down your sender reputation, and enough of them can land your emails in spam instead of the inbox. truemail-go checks an address before you send to it, so you catch the bad ones first.

• Catch bad emails before they hurt your sender reputation.
• Keep your email list clean and your bounce rate low.
• Verify emails before you hit send — protect your deliverability.
• Fewer bounces, better inbox placement. Verify emails first.

It's free and self-hosted: no API keys, no per-lookup billing, no third-party service to trust with your list. It runs on your own server and talks directly to the recipient's mail servers to check whether an address is real.

How it works

It's an HTTP service in Go. Checks an address without sending mail: format, disposable-domain and role-account detection, DNS/MX lookup, and optional SMTP and IMAP probes. Returns a status plus a 0–100 confidence score.

Two services

Service	Lines	What it is
truemail-go-service/	520	The stable service. Per-address rate limiting, configurable bulk concurrency. Start here.
tm2-service/	733	Experimental v2: connection pooling, worker pool, batched bulk. Same API surface. Not as well exercised.

Both expose the same three endpoints and can be run interchangeably.

API

GET /health

{
  "status": "healthy",
  "service": "truemail-go-real",
  "timestamp": "2026-08-05T18:31:49Z",
  "note": "Using real SMTP + IMAP validation with rate limiting"
}

POST /validate

curl -X POST localhost:8080/validate \
  -H 'Content-Type: application/json' \
  -d '{"email":"someone@example.com"}'

{
  "email": "someone@example.com",
  "status": "valid",
  "score": 90,
  "details": "Email validated with SMTP check",
  "validated_at": "2026-08-05T18:00:00Z"
}

POST /validate/bulk

curl -X POST localhost:8080/validate/bulk \
  -H 'Content-Type: application/json' \
  -d '{"emails":["a@example.com","b@example.com"],"fast":true}'

Returns {"results":[ ... ]}. Set "fast": true to skip SMTP probing for the batch.

Status and score

status is one of valid, invalid, unknown, or rate_limited. The score reflects how much of the check chain passed:

Score	Status	Meaning
100	valid	SMTP and IMAP checks passed
90	valid	SMTP check passed
70	valid	Role-based address (info@, admin@) — real, but lower deliverability
60	unknown	Domain and MX valid, SMTP probe failed
40	unknown	Domain valid, no MX records
0	invalid	Bad format, disposable domain, or no DNS
0	rate_limited	Same address queried too soon — retry later

unknown is a real answer, not a failure: many hosts (notably Microsoft 365) accept every RCPT TO, so a failed SMTP probe does not prove an address is dead. Treat unknown as "do not discard."

Configuration

All via environment variables:

Variable	Default	Effect
PORT	8080	Listen port
ENABLE_SMTP_VALIDATION	off	Set true to enable SMTP/IMAP probing. Off = DNS/MX only, much faster
BULK_VALIDATION_CONCURRENCY	built-in	Parallel validations per bulk request
RATE_LIMIT_SECONDS	built-in	Per-address cooldown. 0 disables rate limiting

Run

cd truemail-go-service && go run .

Docker:

cd truemail-go-service
docker build -t truemail-go .
docker run -p 8080:8080 -e ENABLE_SMTP_VALIDATION=true truemail-go

Notes on SMTP probing

• Port 25 is usually blocked on residential ISPs and most cloud providers (AWS, GCP, Azure, DigitalOcean block it by default). Without outbound 25 the SMTP probe always fails and you get unknown results. Run this somewhere with port 25 egress, or leave ENABLE_SMTP_VALIDATION off.
• The probe issues MAIL FROM:<validation@example.com> and never sends a message.
• Probing at volume from one IP gets that IP greylisted or blocklisted. Keep the rate limit on and concurrency modest.
• Verify addresses you have a lawful basis to process. List hygiene on your own opt-in data is fine; scanning lists you acquired elsewhere may not be.

License

MIT — see LICENSE.