SSL/TLS Send Mail

SSL/TLS Send Mail Example

A NetBurner embedded application that demonstrates secure email transmission using SSL/TLS protocols.

Overview

This application illustrates how to send email messages from a NetBurner device to mail servers that require SSL/TLS encryption. The implementation provides a web-based interface for configuring email settings and sending messages securely over HTTPS connections.

Key Features

• SSL/TLS encrypted email transmission
• Web-based configuration interface
• Support for both direct SSL and STARTTLS negotiation methods
• SMTP authentication support
• Network time synchronization via NTP
• File system utilities for external storage devices

SSL/TLS Connection Methods

The application supports two SSL/TLS handshake methods:

Direct SSL Connection

• Connects directly to SSL/TLS ports (465 or 587)
• Uses SSL_connect for immediate secure connection
• Recommended for servers known to support SSL/TLS
• Suitable for services like Yahoo that expect SSL connections on specific ports

STARTTLS Method

• Initially connects to standard SMTP port 25
• Performs EHLO command to check server capabilities
• If server responds with "STARTTLS", initiates SSL negotiation
• Required for Gmail and servers that mandate TLS encryption

Configuration Requirements

Network Setup

• Valid IP address, network mask, gateway, and DNS configuration
• Internet connectivity for NTP time synchronization and mail transmission
• DHCP support available (set IP address to 0.0.0.0 to enable)

Gmail Configuration

When connecting to Gmail accounts:

1. Enable "less secure application access" in account settings
2. For two-factor authentication accounts, create an application-specific password
3. Use server: smtp.gmail.com
4. Use port: 465 or 587
5. Leave STARTTLS unchecked
6. Generate app passwords at: https://myaccount.google.com/apppasswords

Yahoo Configuration

• Requires premium services (mailplus or bizmail) - free accounts not supported
• Does not support STARTTLS detection
• Connect to port 465/587 for SSL or port 25 for non-SSL

Application Structure

Core Components

main.cpp**

• Application entry point and initialization
• Network stack setup and HTTPS server startup
• NTP time synchronization

• System diagnostics enablement

  webfuncs.cpp**

• Web interface implementation
• Form handling for email configuration
• SSL email transmission logic

• Network and DNS management

  index.html**

• Web-based user interface
• Dynamic port selection based on STARTTLS setting
• Network configuration display
• Email form with validation

File System Support

The application includes comprehensive file system utilities supporting:

• SD/MMC cards
• SDHC cards
• Compact Flash (CFC)

• RAM drives

  Supported Operations:**

• File creation, reading, writing, and deletion
• Directory management
• FTP server functionality
• Multiple storage device types

Usage Instructions

1. Network Configuration
   • Verify IP gateway and DNS settings
   • Enable DHCP by setting IP to 0.0.0.0 (optional)
2. Email Configuration
   • Enter mail username and password
   • Specify SMTP server hostname
   • Set appropriate port (25, 465, or 587)
   • Configure STARTTLS if required by server
3. Send Email
   • Fill in sender and recipient addresses
   • Enter subject and message body
   • Click "Send Mail" to transmit

Technical Implementation

Security Features

• SSL/TLS encryption for all mail transmission
• HTTPS web interface
• Secure credential handling
• DNS lookup validation

Error Handling

• Comprehensive DNS failure detection
• SSL connection error reporting
• File system error codes with descriptions
• Network timeout management

Development Requirements

NBEclipse Linker Configuration:** Add libStdFFile.a library:

1. Right-click project, select "Properties"
2. Navigate to "C/C++ Builds -> Settings"
3. Select "GNU C/C++ Linker -> Libraries"
4. Add "StdFFile" to Libraries list

Platform Support

• NetBurner embedded platforms
• Multiple storage device interfaces
• Real-time clock integration
• Timezone management with DST support

Error Codes and Troubleshooting

The application provides detailed error reporting for:

• File system operations (38 defined error codes)
• Network connectivity issues
• SSL/TLS handshake failures
• SMTP authentication problems
• DNS resolution failures