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Troubleshooting Common Post SMTP Plugin Connection and Delivery Errors

31 threads Sep 16, 2025

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If you're using the Post SMTP plugin and encountering issues like 'Connection refused,' emails not arriving, or slow delivery, you're not alone. These are some of the most frequently reported problems by users. This guide will walk you through the common causes and the steps you can take to resolve them.

Common Error Messages and Their Meanings

  • "Connection refused" / "Network is unreachable" / "Could not open socket": These errors typically point to a network-level blockage between your WordPress hosting server and your outgoing mail server (e.g., Gmail, Office 365, Brevo).
  • Emails marked as "Sent" but not received: The connection was successful, but the email was likely rejected or filtered as spam by the recipient's server after it left your site.
  • Slow email delivery: This can be caused by slow DNS resolution, network latency, or performance issues on your SMTP service provider's end.
  • "Ready State 4 error": This is often a server-level issue, frequently related to a security module like ModSecurity blocking the plugin's AJAX requests.

Step-by-Step Troubleshooting Guide

1. Run the Diagnostic Test

The first step for almost any issue is to access the Post SMTP diagnostic tool. This report provides crucial information about your server's environment.

  • Navigate to WordPress Admin > Post SMTP > Dashboard.
  • Click the "Diagnostic Test" tab.
  • Copy the entire report. This is the single most important piece of information to have on hand when seeking help.

2. Investigate Connection Issues ("Connection refused")

If your diagnostic test fails or you see connection errors, follow these steps:

  • Check Hosting Firewalls: Many web hosts, especially shared hosting providers like GoDaddy or Hostinger, block outgoing SMTP connections on non-standard ports. Contact your hosting support and ask if they block outgoing SMTP traffic and which port you should use (e.g., 587, 465, 25).
  • Verify SMTP Settings: Double-check the hostname, port, and encryption type (SSL/TLS) in your Post SMTP settings against the official documentation for your email service (e.g., Gmail, Office 365, Brevo). Note that Brevo recently changed its SMTP URL from smtp-relay.sendinblue.com to smtp-relay.brevo.com.
  • Test with a Socket: In the Post SMTP settings, try switching the 'Socket' option from a default option to 'fsockopen' or 'stream' to see if a different PHP connection method works better with your server.

3. Solve Emails Not Being Received (Sent but Not Delivered)

If the test email works but transactional emails (from forms, registrations) do not, focus here:

  • Ensure Use of wp_mail(): The Post SMTP plugin only works if WordPress or your plugins use the built-in wp_mail() function to send mail. If a plugin or custom code uses the native PHP mail() function directly, Post SMTP cannot intercept it. You may need to modify the code to use wp_mail().
  • Check Spam Folders & DNS Records: If emails are being sent but rejected as spam, you must configure your domain's DNS records. Set up SPF and DKIM records for your domain through your DNS provider. These records tell receiving mail servers that your website is authorized to send email on behalf of your domain, which is critical for inbox placement.
  • Review Email Log: Use the Post SMTP Email Log to see the status of each email. If an email is marked as sent, the issue lies after it left your server.

4. Address "Ready State 4" or Admin Access Errors

  • Contact Your Host: A "Ready State 4" error is almost always caused by the ModSecurity firewall on your server blocking a request from the plugin. You must contact your hosting provider's support, provide them with the error, and ask them to review the ModSecurity logs for false positives.
  • Reinstall the Plugin: If you cannot access the Post SMTP settings page at all ('Sorry, you are not allowed to access this page'), try deactivating and deleting the plugin. Then, reinstall it fresh from the WordPress plugin repository. This can resolve corrupted permission settings.

5. What to Provide When Asking for Help

To get effective help from the community, always include the following information:

  1. Your full Post SMTP Diagnostic Test report.
  2. The exact error message you are seeing.
  3. The name of your SMTP service (e.g., Gmail, Office 365, Brevo).
  4. The Mailer Type and Socket you have configured in the plugin settings.

By methodically working through these common issues, you can identify and resolve most problems with the Post SMTP plugin. The diagnostic report is your best friend in this process, so always start there.

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