Replace Zend_Mail (ZF1) with Zend\Mail\Message (ZF2)

[0m3r]

Zend\Mail\Transport\SMTP almost \Zend_Mail_Transport_Smtp

magento/magento2#8608

In 2.3-develop

"zendframework/zend-mail": "^2.9.0",

https://github.com/magento/magento2/blob/2.3-develop/composer.json#L69

[roma84]

Up,
error in 2.3.0:
Something went wrong while checking the service.The message should be an instance of \Zend_Mail