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It looks like the installation is not completed.
From the error, PDO extension is not enabled on your server. Can you ask your hosting provider to enable this?
Below are all other requirements of TMail, you can try to cross check all with your hosting provider:
After Complete all the extension now its says 404 Not found
I can see the TMail Installer is loaded on the website.
Can you please check?
now working fine
Great. So, all good now?