I need to use custom SMTP settings for my WordPress site to send email through my email servers such as Mailgun or SendGrid.
Place this in your theme function.php or your own plugin.
add_action( 'phpmailer_init', 'custom_phpmailer_init' );
function custom_phpmailer_init( $phpmailer ) {
$phpmailer->isSMTP();
$phpmailer->Host = 'smtp.mailgun.com';
$phpmailer->Port = 465;
$phpmailer->Username = 'user_name';
$phpmailer->Password = '********';
$phpmailer->SMTPAuth = true;
$phpmailer->SMTPSecure = 'ssl';
$phpmailer->From = 'FromName@example.com';
$phpmailer->FromName = 'FromName';
}