Hi PedroN,
even that I have to state clear, that your issue is absolutely not related to any Plesk component, I will still try to help you here.
Your error:
	
	
	
		Code:
	
	
		PHP Fatal error:  Uncaught exception 'phpmailerException' with message 'Invalid address: wordpress@' in /var/www/vhosts/mygamercloud.com/httpdocs/wp-includes/class-phpmailer.php:946
	 
 
	
	
	
		Code:
	
	
		Stack trace:
#0 /var/www/vhosts/mygamercloud.com/httpdocs/wp-includes/pluggable.php(352): PHPMailer->setFrom('wordpress@', 'WordPress')
	 
 ... leads to the fact that the code at "
/var/www/vhosts/mygamercloud.com/httpdocs/wp-includes/pluggable.php" on line 352 has to be corrected.
Line 352 of "
pluggable.php":
	
	
	
		Code:
	
	
		    $phpmailer->setFrom( $from_email, $from_name );
	 
 ... which is the result of line 315 and 331
	
	
	
		Code:
	
	
		        $from_name = 'WordPress';
	 
 
	
	
	
		Code:
	
	
		        $from_email = 'wordpress@' . $sitename;
	 
 
Investigation: "$sitename;" has not been requested correctly and the result is a false eMail - adress => "setFrom('wordpress@', 'WordPress')"
=> the domain-name is missing after the "@".
Suggested fix:
Comment out line 331 and add below:
BEFORE THE CHANGE:
	
	
AFTER THE CHANGE:
	
	
	
		Code:
	
	
		...
/**        $from_email = 'wordpress@' . $sitename;     **/
        $from_email = '[email protected]';
...
	 
 ... where "
YOUR-DOMAIN.COM" should be replaced with a fully qualified domain name ( FQDN ) on your server, able to send eMails.
 
Important note:
This suggested fix is a temporary work - around. Wordpress itself will provide an update/upgrade in the near future, when they investigate themself, that the ". $sitename" is not being added correctly in Wordpress 4.6. Pls. consider to contact Wordpress itself if you have any questions to this issue.