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Environment Variables

GoSMTP-dup can be configured entirely using environment variables with the SMTP_DUP_ prefix.

Environment Variable Format

Environment variables use the prefix SMTP_DUP_ followed by the configuration path with dots replaced by underscores:

smtp.listen → SMTP_DUP_SMTP_LISTEN
relay.destination_primary → SMTP_DUP_RELAY_DESTINATION_PRIMARY

Available Variables

Environment Variable	Config Equivalent	Example Value
`SMTP_DUP_SMTP_LISTEN`	`smtp.listen`	`"0.0.0.0:2525"`
`SMTP_DUP_SMTP_DOMAIN`	`smtp.domain`	`"mail.example.com"`
`SMTP_DUP_RELAY_DESTINATION_PRIMARY`	`relay.destination_primary`	`"primary.example.com:25"`
`SMTP_DUP_RELAY_DESTINATION_BACKUPS`	`relay.destination_backups`	`"backup1.com:25,backup2.com:25"`
`SMTP_DUP_RELAY_TIMEOUT_SECONDS`	`relay.timeout_seconds`	`"30"`

Usage Examples

Shell Export

# Basic configuration
export SMTP_DUP_SMTP_LISTEN="0.0.0.0:2525"
export SMTP_DUP_SMTP_DOMAIN="mail.example.com"
export SMTP_DUP_RELAY_DESTINATION_PRIMARY="primary.example.com:25"
export SMTP_DUP_RELAY_DESTINATION_BACKUPS="backup1.example.com:25,backup2.example.com:25"
export SMTP_DUP_RELAY_TIMEOUT_SECONDS="30"

# Run the application
./gosmtp-dup

Docker Environment

docker run -d \
  --name smtp-duplicator \
  -p 2525:2525 \
  -e SMTP_DUP_SMTP_LISTEN="0.0.0.0:2525" \
  -e SMTP_DUP_SMTP_DOMAIN="mail.example.com" \
  -e SMTP_DUP_RELAY_DESTINATION_PRIMARY="primary.example.com:25" \
  -e SMTP_DUP_RELAY_DESTINATION_BACKUPS="backup1.example.com:25,backup2.example.com:25" \
  -e SMTP_DUP_RELAY_TIMEOUT_SECONDS="30" \
  ghcr.io/cabonemailserver/gosmtp-dup:latest

Docker Compose

version: '3.8'
services:
  smtp-duplicator:
    image: ghcr.io/cabonemailserver/gosmtp-dup:latest
    ports:
      - "2525:2525"
    environment:
      SMTP_DUP_SMTP_LISTEN: "0.0.0.0:2525"
      SMTP_DUP_SMTP_DOMAIN: "mail.example.com"
      SMTP_DUP_RELAY_DESTINATION_PRIMARY: "primary.example.com:25"
      SMTP_DUP_RELAY_DESTINATION_BACKUPS: "backup1.example.com:25,backup2.example.com:25"
      SMTP_DUP_RELAY_TIMEOUT_SECONDS: "30"
    restart: unless-stopped

Kubernetes Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: smtp-duplicator
spec:
  replicas: 1
  selector:
    matchLabels:
      app: smtp-duplicator
  template:
    metadata:
      labels:
        app: smtp-duplicator
    spec:
      containers:
      - name: smtp-duplicator
        image: ghcr.io/cabonemailserver/gosmtp-dup:latest
        ports:
        - containerPort: 2525
        env:
        - name: SMTP_DUP_SMTP_LISTEN
          value: "0.0.0.0:2525"
        - name: SMTP_DUP_SMTP_DOMAIN
          value: "mail.example.com"
        - name: SMTP_DUP_RELAY_DESTINATION_PRIMARY
          value: "primary.example.com:25"
        - name: SMTP_DUP_RELAY_DESTINATION_BACKUPS
          value: "backup1.example.com:25,backup2.example.com:25"
        - name: SMTP_DUP_RELAY_TIMEOUT_SECONDS
          value: "30"

Configuration Priority

Environment variables take precedence over configuration files:

Environment variables (highest priority)
Configuration file (lower priority)
Default values (lowest priority)

Default Values

Setting	Default Value
`smtp.listen`	`"127.0.0.1:2525"`
`smtp.domain`	`"localhost"`
`relay.timeout_seconds`	`10`

Array Values

For array configurations like destination_backups, use comma-separated values:

# Multiple backup servers
export SMTP_DUP_RELAY_DESTINATION_BACKUPS="server1.com:25,server2.com:25,server3.com:25"

# Single backup server
export SMTP_DUP_RELAY_DESTINATION_BACKUPS="backup.example.com:25"

# No backup servers (empty)
export SMTP_DUP_RELAY_DESTINATION_BACKUPS=""

Validation

The application will:

Use default values for missing optional settings
Exit with error if required settings are missing
Log configuration source (file vs environment variables)

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