1. Disable email scanning in your antivirus software settings.
If you are running anti-virus software such as Avast, Kaspersky, or Fortinet, or if you have to use a proxy server to access the internet, these interfere with Inky.
2. Try again after a short while.
In case your Internet connection is down, you can try to establish a connection again once it's up.
3. Wrong server configuration.
Check and update the server information, especially port numbers, as provided by your network administrator.