Function and usage of fix_phpmailer_messageid() in wordpress


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    The fix_phpmailer_messageid() function in WordPress is designed to modify the "From" host in outgoing emails to match the site's domain. This adjustment is crucial in ensuring that emails sent from a WordPress site appear more authentic and are less likely to be flagged as spam. Here's a detailed breakdown of its usage and functionality:


    fix_phpmailer_messageid( PHPMailer $phpmailer )


    This function corrects the "From" host in the email header of outgoing mails. By default, WordPress uses wp_mail() for sending emails which, in turn, uses PHPMailer. The "From" host in the email header often defaults to the server's domain. This can be problematic, especially if the server's domain is different from your site's domain, making the email seem like it's coming from an untrusted or unrelated source. fix_phpmailer_messageid() addresses this by ensuring the email's "From" host matches your site's domain, enhancing the credibility and deliverability of your emails.


    • $phpmailer (PHPMailer, required): This is the instance of PHPMailer being used to send the email. PHPMailer is a popular email sending library in PHP. In the context of WordPress, this object is passed by reference to the function, allowing fix_phpmailer_messageid() to modify the necessary properties directly.

    Sample Usage:

    To use this function, you typically attach it to the phpmailer_init action hook in WordPress. Here's a simple example:

    add_action( 'phpmailer_init', 'custom_fix_phpmailer_messageid' );
    function custom_fix_phpmailer_messageid( $phpmailer ) {
        // Call the fix_phpmailer_messageid function with the PHPMailer instance
        fix_phpmailer_messageid( $phpmailer );

    In this snippet:

    1. You create a custom function custom_fix_phpmailer_messageid that takes a PHPMailer instance as its parameter.
    2. You then add this function to the phpmailer_init action hook, which is triggered right before WordPress sends an email.
    3. Inside your custom function, you call fix_phpmailer_messageid() and pass the $phpmailer object to it. This adjusts the "From" host to match your site's domain.


    Using fix_phpmailer_messageid() helps in aligning your email's "From" host with your site's domain, which is a best practice for email deliverability. This function is particularly useful for sites hosted on a server where the default email domain does not match the site's domain.

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