If you use the default Windows proxy, download the config included in the attachments section 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.

However, this solution only works for eM Client up to version 7.2, not for the newly released eM Client 8.

If you are using a different proxy solution or newer version, 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.