wp-gravity-smtp

Gravity SMTP

WordPress transactional email routing and delivery tracking. Gravity SMTP replaces the unreliable default PHP mail() with direct API integration to your provider — SendGrid, Mailgun, Postmark, Brevo, Amazon SES, Microsoft 365, Google, or custom SMTP.

Required on Elite or Nonprofit Gravity Forms license.

When to use

• Installing or updating Gravity SMTP
• Configuring an email provider (SendGrid, Mailgun, Postmark, etc.)
• Diagnosing failed email delivery or notification issues
• Auditing credential storage (CVE-2026-4020 mitigation)
• Setting up backup senders or delivery alerts
• Verifying email logging in wp-admin

⚠️ CVE-2026-4020 — update immediately

Gravity SMTP ≤ 2.1.4 has an unauthenticated REST endpoint that exposes your mail provider API keys. Update to v2.1.5+ on every environment before any other work.

wp gf version gravitysmtp    # must be ≥ 2.1.5
wp gf update gravitysmtp     # update if needed

Official documentation

Resource	URL
Docs home	https://docs.gravitysmtp.com/
Getting started	https://docs.gravitysmtp.com/getting-started/
Integrations guide	https://docs.gravitysmtp.com/integrations/
User guides	https://docs.gravitysmtp.com/user-guides/
FAQ	https://docs.gravitysmtp.com/faq/
Changelog / releases	https://www.gravityforms.com/gravity-smtp-changelog/
Product page	https://www.gravitysmtp.com/
Pricing (Elite required)	https://www.gravityforms.com/pricing/

Supported providers

Provider	Type	API key source
SendGrid	API	https://app.sendgrid.com/settings/api_keys
Mailgun	API	https://app.mailgun.com/settings/api_security
Postmark	API	https://account.postmarkapp.com/api_tokens
Brevo (Sendinblue)	API	https://app.brevo.com/settings/keys/api
Amazon SES	API	AWS IAM console
Microsoft 365	OAuth	Azure portal
Google / Gmail	OAuth	Google Cloud Console
Custom SMTP	SMTP	Your provider

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Procedure

1) Install and immediately verify version

wp gf install gravitysmtp --activate

# IMMEDIATELY check — CVE-2026-4020
SMTP_VER=$(wp gf version gravitysmtp)
echo "Gravity SMTP: $SMTP_VER"
php -r "exit(version_compare('$SMTP_VER','2.1.5','>=') ? 0 : 1);" \
  || echo "❌ CRITICAL: Update to ≥ 2.1.5"

2) Credential isolation (required)

Store credentials in wp-config.php constants loaded from environment variables. Never store API keys in wp_options — even if CVE is patched, it's better practice.

// wp-config.php
define('GRAVITY_SMTP_SENDGRID_API_KEY', getenv('SENDGRID_API_KEY'));
define('GRAVITY_SMTP_FROM_EMAIL',       getenv('SMTP_FROM_EMAIL'));
define('GRAVITY_SMTP_FROM_NAME',        'U of Digital');

Set the env var in WP Engine (Environment Variables in portal) or via .env locally.

3) Configure in wp-admin

Navigate to: Gravity SMTP (left sidebar) → Settings → choose your provider.

4) Test delivery

# Send a test email via WP-CLI
wp eval "wp_mail('[email protected]', 'Test', 'Gravity SMTP test');"

Check the email log at Gravity SMTP → Email Log.

5) CI/CD — check on every deploy

# In GitHub Actions post-deploy script or wp gf SCRIPT option:
wp gf version gravitysmtp

6) Backup sender + alerts

Configure in Gravity SMTP → Settings → Backup Sender — routes to a fallback if primary fails. Set up Gravity SMTP → Settings → Alerts to get notified on delivery failures.

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Security checklist

# Check version
wp gf version gravitysmtp

# Verify API key is NOT stored in wp_options
wp option get gravitysmtp_sendgrid_api_key 2>/dev/null && \
  echo "⚠️  Key in DB — move to wp-config.php" || echo "✓ Not in wp_options"

References

• wp-gravity-forms skill — Installing GF and add-ons via wp gf
• CVE details: search CVE-2026-4020 on NVD or WPScan