"Unable to send mail" error message when changing user password in Magento Admin (v 2.2.1)

Question

I have a Magento 2.2.1 Running on a Amazon Lightsail VPS (the Bitnami Magento stack).

It has been working just fine, an previously I would get a "Password reset information" e-mail from the system whenever I tried to change the password of a user.

Now, however, if I try to set a new password, the page just reloads with an "Unable to send mail" error message being displayed at the top.

I'm using the SMTP App for Magento 2 plugin to handle mail, and when I go to Stores > Configuration > Advanced > System and test the mail set-up I successfully receive an e-mail from the system.

I have also verified that the e-mail addresses of the user accounts I am trying to reset the password for are valid.

UPDATE, I'm pasting the code from my _sendMail() function below.

    public function _sendMail()
{
    set_error_handler(array($this, '_handleMailErrors'));
    $result = mail(
        $this->recipients,
        $this->_mail->getSubject(),
        $this->body,
        $this->header);
    restore_error_handler();

    if ($this->_errstr !== null || !$result) {
        /**
         * @see Zend_Mail_Transport_Exception
         */
        #require_once 'Zend/Mail/Transport/Exception.php';
        throw new Zend_Mail_Transport_Exception('Unable to send mail. ' . $this->_errstr);
    }
}

Answer 1

If you look at the code, the error is thrown in \Zend_Mail_Transport_Sendmail, in the _sendMail() method, apparently it is still trying to send through the PHP mail() functionality.