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Block Spam Emails by Setting NG Words in Contact Form 7

Block Spam Emails by Setting NG Words in Contact Form 7

Are you troubled by receiving a large number of spam messages through your contact form?

Specifically, spam messages with the following content are frequently being sent:

  • Sales emails, investment solicitations, dating, adult content
  • Strings of English text or nonsensical content
  • Promotional messages containing suspicious links
  • Submissions sent repeatedly in a short time from the same IP address

As a result, there is a risk of missing legitimate inquiries from actual users, and it increases the operational burden.

As countermeasures, we are considering the following approaches:

  • Enhancing the NG word filter
  • Blocking specific IP addresses or domains
  • Implementing reCAPTCHA
  • Spam bot measures such as honeypot functionality

To set NG words (prohibited terms) in Contact Form 7 (CF7), you can implement it using one of the following methods:

✅ Method 1: Add a filter hook to functions.php (Recommended)

Use CF7’s wpcf7_validate_* hook to detect NG words and return a validation error.

Example: Setting NG words for a text field (your-message)

add_filter('wpcf7_validate_textarea', 'custom_ng_word_validation', 10, 2);
function custom_ng_word_validation($result, $tag) {
    $name = $tag->name;

    // Check target field name
    if ($name === 'your-message') {
        $value = isset($_POST[$name]) ? $_POST[$name] : '';

        // List of NG words (add as needed)
        $ng_words = ['Earn money', '100% free', 'Meet singles'];

        foreach ($ng_words as $ng) {
            if (stripos($value, $ng) !== false) {
                $result->invalidate($tag, 'Submission rejected due to suspected spam content.');
                break;
            }
        }
    }

    return $result;
}

✅ Method 2: Example for multiple fields

add_filter('wpcf7_validate_text', 'custom_ng_word_validation_all_fields', 10, 2);
add_filter('wpcf7_validate_textarea', 'custom_ng_word_validation_all_fields', 10, 2);

function custom_ng_word_validation_all_fields($result, $tag) {
    $name = $tag->name;
    $value = isset($_POST[$name]) ? $_POST[$name] : '';

    // List of NG words
    $ng_words = ['Earn money', '100% free', 'Meet singles'];

    foreach ($ng_words as $ng) {
        if (stripos($value, $ng) !== false) {
            $result->invalidate($tag, 'Submission rejected due to suspected spam content.');
            break;
        }
    }

    return $result;
}

🔍 Notes

  • Since stripos() is used, it is case-insensitive.
  • Customize the warning message returned to the sender to match the tone of your site.
  • The * in wpcf7_validate_* corresponds to the field type (text, textarea, email, etc.).

🚀 Advanced Use Cases

  • If NG words should only be rejected on an exact match → use === or in_array()
  • Manage NG words via the database or options page → retrieve them using get_option(), etc.

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