agrisv

And more info:
1. Please enable error throw with “true” – without true no error on failure:

$phpmailer = new PHPMailerOAuth(true); 

2. set email validator to “php”. PHPMailer did it in version 6.x, because much emails are invalid with pcre8 validation. This was also our problem with Ubuntu 18 and php7.3.

$phpmailer::$validator = 'php';

3. Need email retry for timeout connection error for example 3 times, because on network error, email disappear.

4. If you use your own PHPMailer class, maybe need reload class because.. If other plugin initialize PHPmailer class with wordpress default, then you get old version of class and your plugin not work.
example from plugin “woocommerce-pdf-invoices-packing-slips”:

// ww.wp.xz.cn/support/topic/invalid-address-setfrom/#post-11583815
public function set_phpmailer_validator( $mailArray ) {
 if ( version_compare( PHP_VERSION, '7.3', '>=' ) ) {
 global $phpmailer;
 if ( ! ( $phpmailer instanceof \PHPMailer ) ) {
  require_once ABSPATH . WPINC . '/class-phpmailer.php';
  require_once ABSPATH . WPINC . '/class-smtp.php';
  $phpmailer = new \PHPMailer( true );
 }
 $phpmailer::$validator = 'php';
 }

 return $mailArray;
}