Thank you for your question.
Please try accessing localhost:9998 and see if it works. If it does, it's likely that the bindings on the default website were changed.
To resolve this, I recommend deleting the default website and using the SmarterMail site that should have been created during installation. You may also need to update the ports for the SmarterMail site accordingly.
I hope this helps!
Best regards,
Zach Sylvester
Software Developer
SmarterTools Inc.
www.smartertools.com