SMTP server configuration

Host, port, TLS/SSL, timeouts, and provider examples (Gmail, Outlook, and similar) for the SMTP form.

The SMTP functionality is implemented across several key components within the Electron application architecture:

graph TB
subgraph "Electron Application"
UI[React UI Components]
Handler[SMTP Handler]
Main[Main Process]
Preload[Preload Bridge]
end
subgraph "SMTP Components"
SMTPForm[SMTPForm.jsx]
BulkMailer[BulkMailer.jsx]
SMTPHandler[smtp-handler.js]
MainProcess[main.js]
PreloadAPI[preload.js]
end
UI --> SMTPForm
UI --> BulkMailer
SMTPForm --> BulkMailer
BulkMailer --> PreloadAPI
PreloadAPI --> MainProcess
MainProcess --> SMTPHandler
SMTPHandler --> Handler

The SMTP configuration system consists of several interconnected components that work together to provide secure email delivery capabilities:

SMTP configuration form#

The user interface component allows users to configure SMTP server settings including host, port, username, password, and security options.

SMTP handler#

The backend handler manages the actual SMTP connection, authentication, and email sending process using Nodemailer.

IPC communication layer#

The Electron IPC system handles secure communication between the renderer process (UI) and main process (SMTP operations).

SMTP config layers:

sequenceDiagram
participant User as "User Interface"
participant Mailer as "BulkMailer Component"
participant Preload as "Preload Bridge"
participant Main as "Main Process"
participant Handler as "SMTP Handler"
participant Transport as "Nodemailer Transport"
participant SMTP as "SMTP Server"
User->>Mailer : Configure SMTP Settings
Mailer->>Preload : sendSMTPEmail(smtpData)
Preload->>Main : ipcRenderer.invoke('smtp-send', smtpData)
Main->>Handler : handleSMTPSend(event, smtpData)
Handler->>Transport : createTransport(config)
Handler->>Transport : verify()
Transport->>SMTP : Connection Test
SMTP-->>Transport : Connection OK
Transport-->>Handler : Verified
Handler->>Handler : Send Emails Loop
Handler->>Transport : sendMail(options)
Transport->>SMTP : SMTP Transaction
SMTP-->>Transport : Delivery Confirmation
Transport-->>Handler : Success/Failure
Handler-->>Main : Results
Main-->>Preload : Results
Preload-->>Mailer : Results
Mailer-->>User : Progress Updates

SMTP configuration form component#

The SMTP form component is the UI for configuring email server settings:

classDiagram
class SMTPForm {
+Object smtpConfig
+String emailList
+String subject
+String message
+Number delay
+Boolean isSending
+Array results
+setSMTPConfig(config) void
+importEmailList() void
+sendSMTPBulk() void
}
class SMTPConfig {
+String host
+Number port
+Boolean secure
+String user
+String pass
}
class EmailValidation {
+validateEmailFormat(email) Boolean
+extractEmails(input) Array
}
SMTPForm --> SMTPConfig : "manages"
SMTPForm --> EmailValidation : "uses"

SMTP handler implementation#

The SMTP handler manages the complete email sending process with reliable error handling and progress tracking:

flowchart TD
Start([SMTP Send Request]) --> ValidateConfig["Validate SMTP Configuration"]
ValidateConfig --> ConfigValid{"Configuration Valid?"}
ConfigValid --> |No| ReturnError["Return Error Response"]
ConfigValid --> |Yes| CreateTransporter["Create Nodemailer Transporter"]
CreateTransporter --> VerifyConnection["Verify SMTP Connection"]
VerifyConnection --> ConnectionOK{"Connection Verified?"}
ConnectionOK --> |No| ReturnConnectionError["Return Connection Error"]
ConnectionOK --> |Yes| LoopRecipients["Loop Through Recipients"]
LoopRecipients --> SendEmail["Send Individual Email"]
SendEmail --> EmailSuccess{"Email Sent?"}
EmailSuccess --> |Yes| UpdateProgress["Update Progress"]
EmailSuccess --> |No| HandleError["Handle Email Error"]
UpdateProgress --> Delay["Apply Rate Limiting Delay"]
HandleError --> Delay
Delay --> MoreRecipients{"More Recipients?"}
MoreRecipients --> |Yes| LoopRecipients
MoreRecipients --> |No| ReturnSuccess["Return Success Results"]
ReturnError --> End([End])
ReturnConnectionError --> End
ReturnSuccess --> End

IPC communication layer#

The Electron IPC system provides secure communication between the renderer and main processes:

sequenceDiagram
participant Renderer as "Renderer Process"
participant Preload as "Preload Bridge"
participant Main as "Main Process"
participant Handler as "SMTP Handler"
Renderer->>Preload : window.electronAPI.sendSMTPEmail(data)
Preload->>Main : ipcRenderer.invoke('smtp-send', data)
Main->>Handler : handleSMTPSend(event, data)
Handler->>Handler : Process SMTP Operation
Handler-->>Main : Return Results
Main-->>Preload : Return Results
Preload-->>Renderer : Return Results

Gmail SMTP configuration#

Gmail requires specific configuration settings for secure SMTP access:

Outlook/Hotmail SMTP configuration#

Microsoft Outlook requires specific SMTP settings:

Yahoo SMTP configuration#

Yahoo Mail requires specific SMTP configuration:

Custom SMTP server configuration#

For custom SMTP servers, the configuration follows standard patterns:

TLS/SSL configuration options#

SMTP security options the handler exposes:

classDiagram
class SMTPTransportConfig {
+String host
+Number port
+Boolean secure
+Object auth
+Object tls
}
class TLSSettings {
+Boolean rejectUnauthorized
+Array ca
+String servername
}
class SecurityProtocols {
+String STARTTLS
+String SSL
+String TLS
}
SMTPTransportConfig --> TLSSettings : "includes"
SMTPTransportConfig --> SecurityProtocols : "uses"

Certificate validation settings#

The application provides certificate validation flexibility:

• Certificate Validation. Disabled for self-signed certificates (rejectUnauthorized: false)
• Custom CA Certificates. Can be pointed at a private CA
• Hostname Verification. Server name verification for secure connections

Credential storage and security#

The application implements secure credential storage:

• Encrypted Storage. SMTP credentials are stored securely using electron-store
• Selective Storage. Host, port, and user are stored; passwords are not saved
• Memory Management. Credentials are loaded only when needed

Firewall configuration#

SMTP connections require specific firewall configurations:

graph LR
subgraph "Outbound Connections"
SMTPClient[SMTP Client]
Port587[Port 587/TLS]
Port465[Port 465/SSL]
Port25[Port 25/SMTP]
end
subgraph "Firewall Rules"
Allow[Allow Outbound]
Block[Block Inbound]
end
SMTPClient --> Port587
SMTPClient --> Port465
SMTPClient --> Port25
Allow --> Port587
Allow --> Port465
Allow --> Port25
Block -.-> SMTPClient

Network requirements#

The application requires:

• Outbound Access. TCP connections to SMTP servers on configured ports
• DNS Resolution. Ability to resolve SMTP server hostnames
• Time Synchronization. Accurate system time for certificate validation
• Proxy Support. Optional proxy configuration for restricted networks

Rate limiting and throttling#

The system implements intelligent rate limiting:

• Default Delay. 1000ms between email sends
• Configurable Delays. Users can adjust delay intervals
• Provider Limits. Respects provider-specific sending limits
• Backoff Strategies. Gradual increase in delays for failed attempts

Connection timeouts#

The SMTP handler implements detailed timeout mechanisms:

flowchart TD
ConnectionAttempt[SMTP Connection Attempt] --> ConnectTimeout["Connection Timeout (Default)"]
ConnectTimeout --> VerifyTimeout["Verification Timeout"]
VerifyTimeout --> SendTimeout["Individual Email Timeout"]
ConnectTimeout --> ConnectionError[Connection Error]
VerifyTimeout --> VerificationError[Verification Error]
SendTimeout --> SendError[Send Error]
ConnectionError --> RetryAttempts[Retry Attempts]
VerificationError --> RetryAttempts
SendError --> RetryAttempts
RetryAttempts --> MaxRetries{Max Retries Reached?}
MaxRetries --> |No| RetryAttempts
MaxRetries --> |Yes| FinalFailure[Final Failure]

Retry strategies#

The system employs progressive retry strategies:

• Immediate Retry. First failure triggers immediate retry
• Exponential Backoff. Subsequent failures use increasing delays
• Maximum Attempts. Configurable maximum retry attempts
• Error Classification. Different handling for different error types

Progress tracking#

Real-time progress tracking reports status:

• Individual Email Status. Success/failure for each recipient
• Overall Progress. Percentage completion indicator
• Error Details. Specific error messages for failed attempts
• Timing Information. Delivery timestamps and durations

Common SMTP connection issues#

Authentication failures#

• Symptoms. “Authentication failed” or “Invalid credentials”
• Solutions.
  • Verify username/password combination
• Check for App Password requirements (Gmail)
• Ensure two-factor authentication settings are correct

Port blocking issues#

• Symptoms. Connection timeouts or refused connections
• Solutions.
  • Verify firewall allows outbound connections on configured port
• Check with network administrator for blocked ports
• Try alternative ports (587 vs 465)

Certificate validation errors#

• Symptoms. “Certificate verification failed” errors
• Solutions.
  • Check system date/time synchronization
• Verify certificate chain validity
• Point nodemailer at your private CA if you use one

DNS resolution problems#

• Symptoms. “Host not found” or “DNS resolution failed”
• Solutions.
  • Verify SMTP server hostname spelling
• Test DNS resolution using command line tools
• Check network connectivity and DNS server configuration

Network connectivity failures#

Proxy configuration issues#

• Symptoms. Connection timeouts behind corporate firewalls
• Solutions.
  • Configure proxy settings in network preferences
• Verify proxy authentication requirements
• Test proxy connectivity independently

ISP blocking issues#

• Symptoms. Consistent connection failures to specific providers
• Solutions.
  • Contact ISP to unblock SMTP ports
• Use alternative SMTP providers
• Configure SMTP over different ports

Performance and rate limiting issues#

Excessive rate limiting#

• Symptoms. Slow sending speeds or frequent delays
• Solutions.
  • Adjust delay settings in configuration
• Reduce batch sizes for large mailing lists
• Implement staggered sending schedules

Memory and resource issues#

• Symptoms. Application slowdown or crashes during bulk sending
• Solutions.
  • Monitor system resources during operation
• Reduce concurrent connections
• Optimize email content size

Gmail SMTP configuration example#

const gmailSMTPConfig = {
 host: "smtp.gmail.com",
 port: 587,
 secure: false, // Use TLS
 user: "[email protected]",
 pass: "your-app-password"
};

Outlook SMTP configuration example#

const outlookSMTPConfig = {
 host: "smtp-mail.outlook.com",
 port: 587,
 secure: true, // Use SSL
 user: "[email protected]",
 pass: "your-password"
};

Custom SMTP configuration example#

const customSMTPConfig = {
 host: "smtp.yourcompany.com",
 port: 587,
 secure: false, // Use TLS
 user: "[email protected]",
 pass: "your-password"
};

Enterprise SMTP configuration example#

const enterpriseSMTPConfig = {
 host: "smtp.internal.company.com",
 port: 465,
 secure: true,
 user: "[email protected]",
 pass: "enterprise-password",
 tls: {
 rejectUnauthorized: true,
 ca: ["path/to/certificate.pem"]
 }
};

Copy provider host/port from their current docs, not from memory. App passwords and TLS ports change more often than this code does.