All of the above. Things to watch out for:
Obvious spelling or grammatical mistakes are usually a dead giveaway. Mouseover but do not click the links in the email. When you do so, Outlook will display a popup containing the true underlying link. Do the underlying links look phishy? Did you recently perform any actions with the bank or entity in question to prompt this email from them?
Did you get multiple copies of the same or similar emails?
Do you actually do business with this organization?
Is the account number in the mail actually yours? (In the Wells Fargo email at ROI, it was not.)
Are there any attachments? If so, were you expecting to receive an attachment? Its very unlikely that a bank, or any other organization would send you a ZIP file, for example, out of the blue.