Thanks for the notice.
Possibly because of the URL contained in the message and/or as appear to be in html format as composed initially under OE and the copied to another mail client.
Gmail support notice: http://mail.google.com/support/bin/answer.py?hl=en&answer=8253
If our system flags a message as phishing, but you've validated the source from which the message originated, click the down arrow next to Reply at the top-right of the message pane, and select Report Not Phishing to let us know the message is legitimate. And if you receive a message that our phishing detection system doesn't pick up on, click Report Phishing to send a copy of the message to the Gmail Team.