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SMTP2Discord (email-to-Discord webhook)

smtp2discord is a simple SMTP server that resends incoming email to the configured web endpoint (webhook) as a Discord webhook HTTP POST request.

Forwarded message format in Discord:

  • Default format is:
<from>: <subject>
<body>
  • If From header is missing, <from> falls back to SMTP envelope sender (MAIL FROM).
  • If one field is missing, the template omits the unnecessary separator automatically.

Installation

Quick install (all supported OS)

The installer detects your OS, downloads the correct package, installs the service, and prompts for your Discord webhook URL.

curl -fsSL https://raw.githubusercontent.com/MrZoidberg/smtp2discord/master/install.sh | sudo sh

Alpine Linux ships with doas instead of sudo — replace sudo with doas in all commands below.

curl -fsSL https://raw.githubusercontent.com/MrZoidberg/smtp2discord/master/install.sh | doas sh

Supply the webhook URL non-interactively (useful for automated provisioning):

curl -fsSL https://raw.githubusercontent.com/MrZoidberg/smtp2discord/master/install.sh | sudo sh -s -- --webhook https://discord.com/api/webhooks/<ID>/<TOKEN>

Upgrade an existing installation (config is preserved):

curl -fsSL https://raw.githubusercontent.com/MrZoidberg/smtp2discord/master/install.sh | sudo sh -s -- --upgrade

Supported operating systems: Ubuntu, Debian, Alpine, Fedora, Amazon Linux 2023 (x86_64 and arm64).

Manual package install

Download the package for your OS and architecture from the latest release.

Ubuntu / Debian

# Download the .deb (replace version and arch as needed)
curl -LO https://github.com/MrZoidberg/smtp2discord/releases/latest/download/smtp2discord_<version>_linux_amd64.deb

# Install
sudo apt-get install -y ./smtp2discord_*.deb

Fedora

curl -LO https://github.com/MrZoidberg/smtp2discord/releases/latest/download/smtp2discord_<version>_linux_amd64.rpm
sudo dnf install -y ./smtp2discord_*.rpm

Amazon Linux 2023

curl -LO https://github.com/MrZoidberg/smtp2discord/releases/latest/download/smtp2discord_<version>_linux_amd64.rpm
sudo dnf install -y ./smtp2discord_*.rpm

Alpine

Note: Alpine Linux ships with doas instead of sudo. Run commands as root or prefix them with doas.

curl -LO https://github.com/MrZoidberg/smtp2discord/releases/latest/download/smtp2discord_<version>_linux_amd64.apk
doas apk add --allow-untrusted ./smtp2discord_*.apk

Service configuration

After installing, open /etc/default/smtp2discord in your editor and at minimum set the required webhook URL:

sudo $EDITOR /etc/default/smtp2discord
# /etc/default/smtp2discord — required
SMTP2DISCORD_WEBHOOK=https://discord.com/api/webhooks/<ID>/<TOKEN>

# Optional overrides (all have built-in defaults):
# SMTP2DISCORD_LISTEN=:smtp          # listen address (default: :smtp  →  port 25)
# SMTP2DISCORD_NAME=smtp2discord     # SMTP banner name
# SMTP2DISCORD_SMTP_USER=myuser      # AUTH PLAIN credentials (both or neither)
# SMTP2DISCORD_SMTP_PASS_HASH='$2y$10$...'  # bcrypt hash (NOT plaintext)
# SMTP2DISCORD_AUTHOR=               # Discord message username
# SMTP2DISCORD_AVATAR_URL=           # Discord avatar URL
# SMTP2DISCORD_MSG_LIMIT=2097152     # max message size in bytes
# SMTP2DISCORD_TIMEOUT_READ=5        # read timeout (seconds)
# SMTP2DISCORD_TIMEOUT_WRITE=5       # write timeout (seconds)
# SMTP2DISCORD_MESSAGE_TEMPLATE_FILE= # path to custom Go template
# SMTP2DISCORD_DEBUG=false            # enable verbose debug logging
# SMTP2DISCORD_INSECURE_AUTH=false    # allow AUTH on non-TLS connections (use behind TLS proxy)

Then start (or restart) the service:

Init system Start Restart Logs
systemd (Ubuntu, Debian, Fedora, Amazon Linux) sudo systemctl start smtp2discord sudo systemctl restart smtp2discord journalctl -u smtp2discord -f
OpenRC (Alpine) doas rc-service smtp2discord start doas rc-service smtp2discord restart doas logread | grep smtp2discord

Enable auto-start on boot (if not already done by the installer):

# systemd
sudo systemctl enable smtp2discord

# OpenRC (Alpine)
doas rc-update add smtp2discord default

Logging

smtp2discord uses Go's structured logging (log/slog) and writes logs to stdout in text format.

Log levels

Level Content
INFO Server start, one line per successfully forwarded message
ERROR Failures (Discord send errors, server exit)
DEBUG Raw SMTP protocol traces, per-session command events (MAIL FROM, RCPT TO, AUTH, DATA, RSET, QUIT), Discord webhook request details and response status

Enabling debug logging

Set either the flag or the environment variable:

# CLI flag
smtp2discord --debug --webhook=...

# Environment variable (service / Docker)
SMTP2DISCORD_DEBUG=true

In debug mode you will see:

  • Every incoming SMTP connection with its remote address.
  • Each SMTP command (MAIL FROM, RCPT TO, AUTH, DATA, RSET, QUIT) and its outcome.
  • Raw SMTP protocol lines exchanged between client and server.
  • Discord webhook POST details: username, content length, HTTP status code, and response body.

Warning: debug output may contain sensitive information (SMTP credentials, message content). Do not use it in production.

Custom message template

You can override message formatting with --message-template-file.

Template data fields available in Go template files:

  • {{ .From }}
  • {{ .Subject }}
  • {{ .Body }}

Run with custom template file:

  • smtp2discord --webhook=https://discord.com/api/webhooks/<ID>/<TOKEN> --message-template-file=./my-template.tmpl

Docker example:

  • docker run -p 25:25 -v $(pwd)/my-template.tmpl:/templates/my-template.tmpl ghcr.io/MrZoidberg/smtp2discord:latest --webhook=https://discord.com/api/webhooks/<ID>/<TOKEN> --message-template-file=/templates/my-template.tmpl

Example custom template file:

[FROM] {{ .From }}
[SUBJECT] {{ .Subject }}

{{ .Body }}

Dev

  • go build

Dev with Docker

Locally:

  • docker build -f Dockerfile.dev -t smtp2discord-dev .
  • docker run -p 25:25 smtp2discord-dev --timeout.read=50 --timeout.write=50 --webhook=http://some.hook/api

Note: Dockerfile is optimized for GoReleaser dockers_v2 and copies prebuilt binaries from $TARGETPLATFORM/....

The timeout options are optional but make local testing easier with telnet localhost 25.

Here is a telnet example payload:

HELO zeus
# smtp answer

MAIL FROM:<email@from.com>
# smtp answer

RCPT TO:<youremail@example.com>
# smtp answer

DATA
your mail content
.

Docker (production)

Docker images are published to GitHub Container Registry (GHCR):

  • docker pull ghcr.io/MrZoidberg/smtp2discord:latest
  • Minimal required args:
    • docker run -p 25:25 ghcr.io/MrZoidberg/smtp2discord:latest --webhook=https://discord.com/api/webhooks/<ID>/<TOKEN>
  • Full common args:
    • docker run -p 25:25 ghcr.io/MrZoidberg/smtp2discord:latest --name=smtp2discord --listen=:25 --msglimit=2097152 --timeout.read=5 --timeout.write=5 --author="SMTP Bridge" --avatar-url="https://example.com/bot.png" --webhook=https://discord.com/api/webhooks/<ID>/<TOKEN>
  • With SMTP AUTH PLAIN enabled (both required together):
    • docker run -p 25:25 ghcr.io/MrZoidberg/smtp2discord:latest --smtp-user=myuser --smtp-pass-hash='$2y$10$...' --webhook=https://discord.com/api/webhooks/<ID>/<TOKEN>

Required/validation rules:

  • --webhook is required.
  • --smtp-user and --smtp-pass-hash must be provided together (or both omitted).
  • --debug (or SMTP2DISCORD_DEBUG=true) enables verbose logging: raw SMTP protocol traces and Discord webhook request/response details are emitted at DEBUG level.

Docker Compose

services:
  smtp2discord:
    container_name: smtp2discord
    image: ghcr.io/MrZoidberg/smtp2discord:latest
    command: >-
      --name=smtp2discord
      --listen=:25
      --msglimit=2097152
      --timeout.read=5
      --timeout.write=5
      --webhook=https://discord.com/api/webhooks/<ID>/<TOKEN>
    ports:
      - '25:25'
    restart: unless-stopped

SMTP AUTH PLAIN in Compose:

command: >-
  --listen=:25
  --smtp-user=myuser
  --smtp-pass-hash=$$2y$$10$$...
  --webhook=https://discord.com/api/webhooks/<ID>/<TOKEN>

Native usage

  • smtp2discord --listen=:25 --webhook=http://localhost:8080/api/smtp-hook
  • smtp2discord --listen=:25 --smtp-user=myuser --smtp-pass-hash='$2y$10$...' --webhook=http://localhost:8080/api/smtp-hook
  • smtp2discord --help

SMTP AUTH PLAIN

If --smtp-user and --smtp-pass-hash are provided, clients must authenticate before MAIL FROM.

Generate password + bcrypt hash

  1. Generate a strong password (pick one):
# OpenSSL
openssl rand -base64 32 | tr -d '\n'
# Python (no external deps)
python3 -c 'import secrets; print(secrets.token_urlsafe(32))'
  1. Generate a bcrypt hash for --smtp-pass-hash / SMTP2DISCORD_SMTP_PASS_HASH (example, cost 10):
htpasswd -bnBC 10 "" "mypass" | tr -d ':\n'

If you don’t have htpasswd installed, you can generate the same hash using Docker:

docker run --rm httpd:2.4-alpine htpasswd -bnBC 10 "" "mypass" | tr -d ':\n'

Set it in your service config (recommended quoting because bcrypt hashes contain $):

SMTP2DISCORD_SMTP_USER=myuser
SMTP2DISCORD_SMTP_PASS_HASH='$2y$10$...'

Example session:

EHLO localhost
AUTH PLAIN AG15dXNlcgBteXBhc3M=
MAIL FROM:<email@from.com>
RCPT TO:<youremail@example.com>
DATA
your mail content
.

Contribution

Original repos from @alash3al and @donserdal

About

A tiny software that receive a smtp request (email) and send it to Discord webhook

Topics

discord smtp smtp-relay discord-webhook

Resources

Readme

License

Apache-2.0 license
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Releases 8

v0.0.8 Latest
Mar 3, 2026
+ 7 releases

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