magento2 – Magento 2.3.4 Unable to send mail

I am facing quite known issue about sending mail via TransportBuilder. I need to send mail in observer, however each time I try I get error Unable to send email. Unknown error . I can reject any server configuration, because email mechanizm is working in any other way ( orders, registration, newsletter etc. ), so I belive there must be something wrong with my code. Also my $transportBuilder construction is almost copied from other modules .
1.) I’ve created template in etc/email_templates.xml
2.) I’ve created template in view/frontend/email
3.) My $transportBuilder is looking like this


        $transport = $this->transportBuilder
            ->setTemplateIdentifier($templateId) // passed from id in email_templates.xml
            ->addTo($customerEmail, $customerName)
                    'area' => Area::AREA_FRONTEND,
                    'store' =>  $storeId,
                'customer' => $customer


I’ve noticed error is thrown at /vendor/magento/module-email/Model/Transport.php:101 , excalty by zend vendor/zendframework/zend-mail/src/Transport/Sendmail.php:mailHandler() , however no more specific error message is shown.
I am sure that my local enviroment is working good as other mails are sent properly. Maybe I’ve missed something in my new module ? I’ve spent many hours on this issue and I am still stuck, so I’ll be very grateful for some help.