If your internet connection uses proxy then synchronizing with cloud services or receiving mail requires filling in the proxy server settings in EssentialPIM. Proxy server settings are available in Tools -> Options -> Proxy.
Proxy server - enables/disables use of a proxy server.
Type - sets the proxy server type: HTTP/HTTPS, SOCKS4 or SOCKS5.
Requires authentication - use only if your proxy server requires authentication, otherwise leave empty.