If you use the default Windows proxy, download the config included in attachments of this article.

Copy it into the eM Client folder in C:\Program Files (x86).

This config file should then enable the program to detect the needed credentials for your proxy.

 

If you are using a different proxy solution, you need to either arrange for eM Client to get the credentials using a 3rd party program (e.g.Proxifier) or add eM Client to exceptions.