Isso está disponível no arquivo config.php que está sob a pasta / lists / config
Desça até as configurações do mailer
Procure o código a seguir e modifique seu nome de host smtp. Espero que isso ajude.
# If you want to use the PHPMailer class from phpmailer.sourceforge.net, set the following
# to 1. If you tend to send out html emails, it is recommended to do so.
define("PHPMAILER",1);
# To use a SMTP please give your server hostname here, leave it blank to use the standard
# PHP mail() command.
define("PHPMAILERHOST",'');
# if you want to use smtp authentication when sending the email uncomment the following
# two lines and set the username and password to be the correct ones
#$phpmailer_smtpuser = 'smtpuser';
#$phpmailer_smtppassword = 'smtppassword';