SMTP Relay To Microsoft Graph Middleware - Proxy

Overview

This middleware allows applications using legacy Basic Authentication to send emails via Microsoft Graph API.

It includes support for BCC recipients and consolidates emails sent to different recipient types (To, CC, and BCC) to ensure the email is processed and sent only when the QUIT command is issued.

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Configuration

To configure the application, you need a config.ini file in the same folder as the app. Below is an example template:

[MicrosoftGraph]
TenantID = <YourTenantId>
ClientID = <YourClientId>
ClientSecret = <YourClientSecret>
Scope = https://graph.microsoft.com/.default

[Server]
SMTPPort = 2525
Host = 127.0.0.1

Example config.ini File

[MicrosoftGraph]
TenantID = abc123.onmicrosoft.com
ClientID = 11111111-2222-3333-4444-555555555555
ClientSecret = supersecretkey
Scope = https://graph.microsoft.com/.default

[Server]
SMTPPort = 2525
Host = 127.0.0.1

• The default SMTP port is 2525.
• Ensure the TenantID, ClientID, and ClientSecret are properly set for your Microsoft Graph configuration.

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Local Testing & Deployment

Windows

1. Debug/Run Locally

Simply build and run the application:

go build -o smtpservice.exe
./smtpservice.exe

The application will run as a standalone app.

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2. Install as a Windows Service

You can install the application as a Windows service either using the built-in installer logic or manually using sc.exe.

Automatic Installation:

Run the following command:

smtpservice.exe install <serviceName> <displayName> <description>

Example:

smtpservice.exe install MySMTPService "SMTP Relay Server" "Relays emails through Graph API"

This registers the service as MySMTPService in the Windows Services Manager with the specified display name and description.

Manual Installation (Using sc.exe):

Alternatively, to manually create the service:

1. Open the Command Prompt (Admin).
2. Run the following command:

   sc create MySMTPService binPath="C:\path\to\smtpservice.exe" DisplayName="SMTP Relay Server"

3. Start the service:

   sc start MySMTPService

You can also manage the service using the Services Manager GUI:

• Press Win + R, type services.msc, and press Enter.
• Locate your service (SMTP Relay Server), then choose Start, Stop, or configure it.

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3. Start/Stop the Service

Use the Service Control Manager or run the following commands:

Start the service:

sc start MySMTPService

Stop the service:

sc stop MySMTPService

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4. Remove the Service

You can remove the service using the application's built-in uninstall logic or sc.exe.

Using the Application:

smtpservice.exe remove MySMTPService

Using sc.exe:

sc delete MySMTPService

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Linux

Use Systemd for Linux Service Management

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Step 1: Place the Binary

Transfer your compiled binary to /usr/local/bin:

sudo mv smtpservice /usr/local/bin/

Make sure the binary is executable:

sudo chmod +x /usr/local/bin/smtpservice

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Step 2: Create a Systemd Unit File

Create a service file for systemd in /etc/systemd/system/smtpservice.service:

sudo nano /etc/systemd/system/smtpservice.service

Add the following content:

[Unit]
Description=SMTP Relay Server
After=network.target

[Service]
ExecStart=/usr/local/bin/smtpservice
Restart=always
RestartSec=5
User=nobody                # Change this to the appropriate user
Group=nogroup              # Change this to the appropriate group
WorkingDirectory=/usr/local/bin/

[Install]
WantedBy=multi-user.target

Notes:

• Replace User and Group with the appropriate user/group if required (e.g., smtp user).
• ExecStart must point to the absolute path of your binary.

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Step 3: Reload and Start the Service

1. Reload the systemd daemon to recognize the new unit file:

   sudo systemctl daemon-reload

2. Enable the service to start at boot:

   sudo systemctl enable smtpservice

3. Start the service:

   sudo systemctl start smtpservice

4. Check the status of the service:

   sudo systemctl status smtpservice

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Step 4: Logs

To view logs for the service, use:

sudo journalctl -u smtpservice

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Step 5: Remove the Service

To uninstall the service:

1. Stop the service:

   sudo systemctl stop smtpservice

2. Disable it:

   sudo systemctl disable smtpservice

3. Remove the systemd unit file:

   sudo rm /etc/systemd/system/smtpservice.service

4. Reload systemd:

   sudo systemctl daemon-reload

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Cross-Compile

To cross-compile the application for Linux from a Windows development machine, use one of the following methods:

For Linux (x86-64 architecture):

1. Command Prompt (cmd):

set GOOS=linux
set GOARCH=amd64
go build -o smtpservice

2. PowerShell:

$env:GOOS="linux"
$env:GOARCH="amd64"
go build -o smtpservice

3. Git Bash or WSL:

GOOS=linux GOARCH=amd64 go build -o smtpservice

For ARM Architecture:

If targeting ARM (e.g., Raspberry Pi):

GOOS=linux GOARCH=arm GOARM=7 go build -o smtpservice

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Troubleshooting

Common Issues

1. Permission Denied (Linux or Windows):

• Linux: Run commands with sudo to avoid permission issues when managing services.
• Windows: Ensure the application is launched as an Administrator.

2. Service Fails to Start:

• Check the application logs (journalctl -u smtpservice on Linux or Windows Event Viewer).
• Verify that config.ini exists and is configured correctly.

3. Missing config.ini File:

• Ensure config.ini is in the same directory as the application.

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Contributing

We welcome contributions to this project! Please refer to the LICENSE file for more details on how you can contribute.

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License

This project is licensed under the terms of the MIT License. See the LICENSE file for more details.

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Support

For support and feature requests, please open an issue in the repository's issue tracker.