Master SMTP Documentation

Master SMTP is a professional SMTP solution for WordPress with multi connection sending, smart sender rules, routing, logs, reports, and deliverability tools. It replaces the default wp_mail sending with reliable SMTP connections and rule-based control.

Overview

What Master SMTP does

Send all WordPress emails through SMTP (instead of PHP mail).
Create multiple SMTP connections (primary and backup).
Route different email types to different connections.
Apply Smart From Rules (From name, From email, Reply-To) by conditions.
Log emails and view failures with actionable error details.

Typical use cases

Separate transactional emails (orders, password resets) from marketing emails.
Use a backup SMTP provider automatically if primary fails.
Use different sender identities for support, store, and admin emails.
Debug delivery issues with logs, error codes, and source detection.

Requirements

WordPress 5.8+ (recommended: latest stable).
PHP 7.4+ (recommended: 8.1+).
Outbound SMTP ports allowed by your host (commonly 587 or 465).
Valid SMTP credentials from your email provider.

Hosting notes

Many hosts block port 25. Prefer port 587 (STARTTLS) or 465 (SSL).
If your server blocks outbound SMTP, ask hosting support to allow your provider’s SMTP ports.

Installation

Go to WordPress Admin → Plugins → Add New.
Upload the Master SMTP ZIP file and install it.
Activate the plugin.
Open Settings → Master SMTP to start setup.

Quick Start

Go to Settings → Master SMTP → Connections.
Click Add Connection.
Enter your SMTP host, port, encryption, username, and password.
Set this connection as Primary.
Go to Test Tools and send a test email.
Check Email Logs to confirm sending and review details.

MasterSMTP Dashboard

The dashboard provides a quick view of sending activity and connection health.

Common widgets

Sent today, sent this week, failed, retried.
Top sources (WooCommerce, forms, WordPress core, other plugins).
Top senders (From addresses and identities).
Connection health (last test, last failure, status indicator).

Recommended actions

Run a quick SMTP test after configuration changes.
Review failed logs first, then check routing rules.
Enable debug mode only when troubleshooting.

Connections

A connection is a saved SMTP profile. You can create multiple connections and choose which one is used based on routing rules.

Create a connection

Open Connections.
Click Add Connection.
Fill in the SMTP details.
Save the connection.
Use Test Tools to validate sending.

Connection fields

Name: Internal label (example: Primary SMTP, Backup SMTP).
Host: SMTP server (example: smtp.yourdomain.com).
Port: Common values: 587 (STARTTLS) or 465 (SSL).
Encryption: None, STARTTLS, or SSL.
Authentication: Enables username and password login.
Username: Often the full email address.
Password: Password or app password, depending on provider.
From Email (default): Default sender email for this connection.
From Name (default): Default sender name for this connection.
Force From: Override From set by themes and plugins.
Reply-To (default): Default reply address.
Timeout: Connection timeout in seconds.
Debug Mode: Adds detailed technical output to logs (use temporarily).

Primary and backup

Primary: Used when no routing rule matches.
Backup: Used when sending fails on the selected connection (if fallback is enabled).

Routing and Priorities

Routing decides which connection is used for a specific email. Rules are checked from top to bottom, first match wins.

Common routing conditions

Email type: password reset, new user, comment notice, WooCommerce order.
Source plugin: WooCommerce, Elementor Forms, Contact Form 7, WP core.
Recipient: invoices@, support@, admin@.
Subject contains: keywords like “Order”, “Invoice”, “Support”.
Headers include: detect plugin headers when available.

Recommended rule order

Critical transactional (orders, payments, password resets).
Support and contact forms.
Admin notifications.
Marketing, newsletters.
Fallback behavior and defaults.

Fallback and retries

Fallback: Retry with a secondary connection if sending fails.
Retries: Immediate retry, then delayed retries (based on your settings).
Stop policy: Stop after N attempts and mark as failed.

Smart From Rules

Smart From Rules let you dynamically set From Name, From Email, and Reply-To based on conditions, without changing each plugin’s settings.

What Smart From Rules can set

From Name
From Email
Reply-To
Return-Path (when supported by the provider)
Custom headers (optional)

Common Smart From conditions

By email type: orders, password resets, form notifications.
By source plugin: WooCommerce, Elementor Forms, CF7, WPForms, Fluent Forms.
By recipient: sales vs support routing.
By subject keywords: “Invoice” vs “Ticket”.

Example Smart From setups

Transactional: From Email [email protected], From Name Your Store, Reply-To [email protected]
Support: From Email [email protected], From Name Support Team, Reply-To [email protected]
Marketing: From Email [email protected], From Name Your Brand, Reply-To [email protected]

Email Logs

Email Logs store sending attempts and results, so you can troubleshoot and audit email activity.

What gets logged

Status: sent, failed, queued, retrying.
Timestamp, connection used, fallback used.
To, CC, BCC, subject.
Source detection (plugin or email type, when possible).
SMTP response codes and messages (when available).

Optional logging options

Log only failures (recommended for most sites).
Log full headers (helpful during debugging).
Log body preview (disable unless required, may store personal data).
Log attachments metadata (names and sizes, not contents).

Retention and cleanup

Set retention (example: 7, 14, 30 days).
Automatic cleanup runs via WP-Cron.

Filters and search

Filter by status, date range, connection, recipient, subject keyword.
Start with Failed logs to diagnose problems faster.

Reports and Analytics

Reports summarize sending volume and errors to help you spot deliverability issues early.

Available reports

Daily, weekly, monthly sending totals.
Failure rate over time.
Failures by connection and error code.
Top sources and top subject patterns.
Average send time (SMTP latency).

Export

Export logs and reports to CSV.
Export filtered data (example: failed emails last 7 days).

Test Tools

Use Test Tools to verify connectivity and confirm that routing and sender rules behave as expected.

Send a test email

Go to Test Tools.
Select a connection (or use Primary).
Enter a recipient address you can check.
Send the test email.
Open Email Logs to review the full result.

Connection diagnostics

DNS lookup for the SMTP host.
Basic connectivity checks (best effort, depends on server permissions).
TLS handshake details (when available).
Authentication validation (when provider supports it).

Deliverability Checklist

SMTP solves sending reliability. Deliverability also needs domain alignment and reputation.

DNS records to configure

SPF: authorizes sending servers for your domain.
DKIM: signs outgoing email to prove authenticity.
DMARC: tells receivers how to handle SPF and DKIM failures.

Sender alignment rules

Use a From Email on a domain you control.
Match From Email with the authenticated domain used by your SMTP provider.
Avoid using random From addresses set by third party plugins.

Alerts and Webhooks

Alerts

Notify admin when failures exceed a threshold.
Notify on connection authentication errors.
Optional daily failure summary.

Webhooks

Webhooks can push mail events to external systems (Slack, Discord, Zapier, custom endpoints).

Events: mail_sent, mail_failed, mail_retried, connection_down.
Payload can include timestamp, connection, subject, recipient, and error details.

Security and Privacy

Credentials

Use app passwords when required by your email provider.
Limit access to Master SMTP settings to trusted administrator roles.
Enable debug and detailed logging only when necessary.

Privacy

Logging full bodies can store personal data, keep it disabled unless needed.
Use short retention periods when logs contain sensitive information.
Export logs only when needed and remove exported files after use.

Performance and Reliability

Queue mode (optional)

Queue emails for background sending on high traffic sites.
Reduce page load delays caused by SMTP latency.
Control batch size and rate limits.

Throttling and limits

Set per connection rate limits to avoid provider blocks.
Use retries for temporary errors and fallback for provider outages.

Integrations

Master SMTP works with wp_mail, so most plugins are supported automatically.

Common sources

WooCommerce: orders, refunds, invoices.
Elementor Forms: notifications and confirmations.
Contact forms: CF7, WPForms, Fluent Forms, Gravity Forms.
Membership plugins: account and renewal emails.
Security plugins: alerts and notifications.

Migration

Move from another SMTP plugin

Create a Master SMTP connection with the same SMTP values you currently use.
Send a test email and confirm logs show success.
Disable the old SMTP plugin to avoid conflicts.
Enable logs for a short period to confirm stability.

Troubleshooting

Emails show “sent” but do not arrive

Check spam, promotions, and quarantine folders.
Verify SPF, DKIM, and DMARC for the From domain.
Check that From Email is aligned with the authenticated domain.
Test delivery to multiple providers (Gmail, Outlook, custom domain).

Authentication failed

Recheck username and password (watch for extra spaces).
Use an app password if the provider requires it.
Confirm SMTP authentication is enabled on the mailbox.

Could not connect to SMTP host

Verify host and port.
Switch between 587 (STARTTLS) and 465 (SSL) depending on provider guidance.
Ask hosting support about blocked outbound SMTP ports.

TLS and certificate errors

Confirm the server time is correct.
Try a different encryption mode (STARTTLS vs SSL) if the provider supports it.
Update server certificates (hosting level).

Common SMTP error codes

535: authentication failed, check credentials or app password.
550: rejected, check recipient exists or sender policy blocks.
421: temporary unavailable, enable retries or reduce rate.
451: temporary local problem, retry later.
554: transaction failed, policy or content issue, check sender alignment and message content.

FAQ

Does Master SMTP work with my plugin?

Yes in most cases. If the plugin sends emails using WordPress wp_mail, Master SMTP can handle it.

Should I enable Force From?

Enable it when plugins or themes set incorrect From addresses, or when you need consistent sender identity site wide.

Can I use multiple senders?

Yes. Use Smart From Rules to change From Name, From Email, and Reply-To based on source, email type, or recipient.

Will this guarantee inbox delivery?

No plugin can guarantee inbox placement. Master SMTP improves sending reliability and gives you the tools to configure proper authentication and track issues.

Glossary

Connection: saved SMTP profile used to send mail.
Primary: default connection when no rule matches.
Fallback: backup connection used after a failure.
Routing Rule: rule that selects which connection to use.
Smart From Rule: rule that sets sender identity fields.
SPF: DNS record authorizing senders for your domain.
DKIM: cryptographic signature proving domain authenticity.
DMARC: policy describing how receivers handle failed SPF or DKIM checks.

Changelog

v1.0.0

Initial release: connections, routing, Smart From Rules, logs, reports, test tools.

Planned improvements

Advanced queue and throttling controls.
More routing conditions and stronger source detection.
Expanded webhook events and notification channels.
Enhanced deliverability checks and setup hints.