Flagged? just received an e-mail but I’m not sure if I should open it?

Have been receiving loads of suspicious mail recently, Phishing sites ie MSN asking for my password, Banca di Roma asking for my account details and Paypal asking for passwords. These have all been sent to a hotmail account. For this reason I am currently suspicious of all mail I receive, and have just received one at yahoo. I have not yet opened it, but it has a symbol of a blue flag next to it, indicated that it is flagged. What does this mean? Senders name is Sender and subject is subject. Have spent all day removing a keylogger from my pc, so don’t want to install another !! Any advice??
Yes but what does flagged mean???

Flagged means this

http://www.tech-recipes.com/rx/1085/outlook_2003_flagging_emails_for_better_productivity

Spot80 – Pubblicità Banca di Roma con P. Villaggio Regia F. Fellini Sogg. Leone in cantina (1993)