Emails not translated into graphics

My email client is Window Live Mail 2009 (WLM). As you know, the Internet is a text-only medium; everything crossing it must be encoded into a series of letters, numbers and symbols. It's up to the receiving end to decode it so it makes sense. I have recently been getting commercial emails that when viewed in WLM have failed to decode back to the text and pictures that should be there. For example, here's what I see in the first part of one of those emails:

Cgo8ZGl2IHN0eWxlPSJ0ZXh0LWFsaWduOmNlbnRlciI+Cgo8YSBocmVmPSJodHRwOi8vbWlteWl3
eS5hY2FkZW1pY3ZpZGVvY29tLmNvbS9WZWx6OG1VY1AvWVN2SGNEc19YUFghUTVBITFfTFZEajhM==

When I view this email on the Comcast server, it's perfect. It is also perfect if I download it into Thunderbird. So, why does it not decode in WLM? The default encoding is set for Western European (ISO) and WLM does not provide any other choices.