Swift_TransportException: Connection could not be established with host
Confirm if you are using the correct parameters to connect your web application with the email account.
Even if you are sure to be using the correct parameters, please double-check just in case. The parameters necessary to connect to your Email Account, depending on the software vendor (e.g., cPanel, Directadmin), may change from time to time, either for technical, security or any other reasons.
The last time we were contacted because of this issue, we gave the same suggestion mentioned above. Our client was able to fix the problem after updating the parameters necessary to connect with the email account.
If the parameters to connect with the email account are correct, and you still require assistance, please contact us.