I´d like to get som simple .cap reader to install on my view machine and dont feel like installing full wireshark since i just need to open and diagnose existing .eml .cap files ...

Mail Viewer lets you access mail databases from Microsoft Outlook Express 4, 5, and 6; Windows Mail/Windows Live Mail; and Mozilla Thunderbird, as well as single EML files.

It reads EML files, and it can import Outlook Express DBX files, turning the contents into EMLs. But if you’re not going to use it as a mail client, there are simpler solutions. One of them is ...