Magneto 2.3 SMTP configured but mails not send

after setting up SMTP extension ,when send test mail giving error “Unable to send mail:unknown error” and
in exception log gives bellow exception.

” main.CRITICAL: Unable to send mail: Unknown error
{“exception”:”[object]
(MagentoFrameworkExceptionMailException(code: 0): Unable to send
mail: Unknown error at
/var/www/magento/app/code/Magento/Email/Model/Transport.php:104,
LaminasMailTransportExceptionRuntimeException(code: 0): Unable
to send mail: Unknown error at
/var/www/magento/vendor/laminas/laminas-mail/src/Transport/Sendmail.php:306)”}
[] “

what would be the reason, and how could I get out of this.. Thank you.