I also tryed
plesk bin extension --exec letsencrypt cli.php --cert-name YOUR-DOMAIN.com -d www.YOUR-DOMAIN.com -d webmail.YOUR-DOMAIN.com -d mail.YOUR-DOMAIN.com -d smtp.YOUR-DOMAIN.com -d pop3.YOUR-DOMAIN.com -d imap.YOUR-DOMAIN.com --email
[email protected] --expand
in my server (centos 6.8 with...