unable to send mail (also test mail)

Replies: 1

Versions:
WordPress: 4.9.6
WordPress MS: No
PHP: 5.6.30-12~ubuntu16.04.1+deb.sury.org+1
WP Mail SMTP: 1.2.5

Params:
Mailer: mail
Constants: No

Server:
PHP.mail(): Yes
Apache.mod_security: No