WP notification emails not working

I have an issue related to email notifications since I moved to a new Brazilian host due to difficulties of host support. Actually, my host is the best of all in Brazil (Locaweb).

Every time I need to upgrade WP, WP stops sending notification emails. The only way to make it work, is installing the plugin WP-MAIL-SMTP, creating a specific email account for this purpose and making a modification to the file “/public_html/wp-includes/class-phpmailer.php” as described below:

protected function smtpSend($header, $body) {
(...)

     if ('' == $this->Sender) {
          $smtp_from = $this->From;
     } else {
          $smtp_from = $this->Sender;
     }
     //Modification (Begin) - Line of code added
     $smtp_from = "contato@emailaccountdomain.com.br
     //Modification (End) - Line of code added

(...)

Note that, PHP function mail() is activated on the host and working as well.