Fallback & Reliability

SendGrail implements a cascading fallback system to maximize email delivery reliability. If the primary SMTP connection fails, SendGrail automatically tries alternative methods before giving up.

How the Fallback Cascade Works

When SendGrail attempts to send an email, it follows this sequence:

1. Primary SMTP Connection (Default Connection)
   |
   |-- Success -> Email delivered, log result
   |-- Failure --v
   |
2. Fallback SMTP Connection (if configured)
   |
   |-- Success -> Email delivered, log result
   |-- Failure --v
   |
3. WordPress Default Mail (if enabled in settings)
   |
   |-- Success -> Email delivered, log result
   |-- Failure --v
   |
4. Log failure, send admin notification (if enabled)

At each stage, if sending succeeds, the process stops and the result is logged. If it fails, the next method in the cascade is attempted.

Configuring the Fallback Connection

1. Navigate to SendGrail > Settings > General.
2. Select a connection from the Fallback Connection dropdown.
3. Optionally enable WordPress Default Mail as a last resort.
4. Click Save Settings.

TIP

For maximum reliability, use a different SMTP provider for your fallback connection. If your primary provider (e.g., SendGrid) has an outage, a fallback on a different provider (e.g., Gmail) is far more likely to succeed than two connections on the same service.

WordPress Default Mail

When the WordPress Default Mail toggle is enabled in General settings, SendGrail will attempt to send the email using PHP's native mail() function as a last resort after both SMTP connections have failed.

This is not recommended as a primary strategy since mail() has all the deliverability problems that SendGrail exists to solve. However, it can serve as an emergency fallback for critical emails like password resets.

WARNING

WordPress default mail relies on your server's PHP mail() configuration. On many shared hosting environments, this function is restricted or disabled entirely. Do not rely on it as your only fallback.

Failure Notifications

When an email fails to deliver through all available methods, SendGrail can notify the site administrator. Enable this under Settings > Notifications > Failure Alerts.

Preventing Notification Loops

A natural concern is: what happens if the notification email itself fails? SendGrail handles this with specific safeguards:

• Failure notification emails are sent through the fallback connection if one is configured, not the primary connection that just failed.
• If no fallback connection is available, the notification is sent via WordPress default mail (mail()), bypassing the SMTP pipeline entirely.
• If the notification email itself fails, the failure is logged but no additional notification is generated. This breaks the potential infinite loop.

Logging Fallback Events

Every step of the fallback cascade is recorded in the email log. Each log entry includes:

• Which connection was attempted.
• Whether it succeeded or failed.
• The error message (if applicable).
• Which method ultimately delivered the email (or that all methods failed).

This gives you full visibility into delivery attempts, making it straightforward to diagnose intermittent provider issues.

Best Practices

• Use two different providers. A fallback on the same provider as your primary does not protect against provider-level outages.
• Test your fallback. Temporarily set an invalid password on your primary connection and send a test email. Verify that the fallback picks up delivery.
• Monitor failure notifications. If you start receiving frequent failure alerts, investigate the primary connection rather than relying on the fallback long-term.
• Keep WordPress default mail as a last resort. Enable it for critical emails, but do not depend on it for reliable delivery.