I received a personal invitation from somebody called "Stephen" this morning which like all emails, loads in an application called Mailwasher Pro which I have installed. That allows me to read the contents straight off my ISP's mailserver without having to download it first to my own machine. There's also a freebie version called Mailwasher Free incidentally.
Since I don't know anybody by that name, I checked out the headers which can also be displayed in Mailwasher and found the name of the company called Zorpia it originated from. Here's the Wikipedia article for it: http://en.wikipedia.org/wiki/Zorpia
There's some useful advice in the Wiki article of how to manage gmail security if you've got an email account there, but as you can see from the references at the foot of the article, getting on their mailing list is something to be avoided like the plague.