Relevant and coincidental personal anecdote:
10 years ago I caught my x-wife in an affair as she was using this same method the communicate with her lover. Her choice of email address for the shared account raised alarms on my firewall, so it was a simple matter to track to her machine. While she had gone to the similar trouble to delete all records on Yahoo (coincidentally), she had been browsing with IE which, due to some off-line setting, was cacheing locally all of the pages she had written. It was simply a matter of laying hands on her laptop and downloading all of that cache to expose the ruse.<p>I cannot find the article, but I believe this method of sharing access to one e-mail account to many parties was one of the comms methods employed by the 9/11 terrorists, pioneered by Columbian drug lords.