Different wp_mail_from and wp_mail_from_name for specific situations

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There are two ways:

  1. Inspect the original value, and if it specific for this case return a specific new value.

  2. Chain the filters: register the mail filter only on specific hooks. So you have to find a hook that happens before wp_mail() is called.

Simple example, not tested, just a guide:

// change mod mails for new comments
add_filter( 'pre_option_moderation_notify', array ( 'WPSE_Mail_Filter', 'init' ) );
// new user registration
add_filter( 'load-user-new.php', array ( 'WPSE_Mail_Filter', 'init' ) );

class WPSE_Mail_Filter
{
    protected static $new_mail = NULL;
    protected static $new_name = NULL;

    public static function init( $input = NULL )
    {
        if ( 'pre_option_moderation_notify' === current_filter() )
        {
            self::$new_mail="[email protected]";
            self::$new_name="Comments at Example.com";
        }

        if ( 'load-user-new.php' === current_filter() )
        {
            self::$new_mail="[email protected]";
            self::$new_name="Users at Example.com";
        }

        // add more cases
        // then check if we set a new value:

        if ( ! empty ( self::$new_mail ) )
            add_filter( 'wp_mail_from', array ( __CLASS__, 'filter_email' ) );

        if ( ! empty ( self::$new_name ) )
            add_filter( 'wp_mail_from_name', array ( __CLASS__, 'filter_name' ) );

        // we do not change anything here.
        return $input;
    }

    public static function filter_name( $name )
    {
        remove_filter( current_filter(), array ( __CLASS__, __FUNCTION__ ) );
        return self::$new_name;
    }

    public static function filter_email( $email )
    {
        remove_filter( current_filter(), array ( __CLASS__, __FUNCTION__ ) );
        return self::$new_mail;
    }
}

The difficult part is finding the proper hook.

For example when a new comment has been written, the function wp_notify_moderator() is called. There is no really good hook in that function, but it calls …

if ( 0 == get_option( 'moderation_notify' ) )

… early. That again fires the hook pre_option_moderation_notify, and that is where we can start our filter. You have to search through the core code to find the best start hook for all cases, but usually there is always something.

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