One of the most common ways that hackers and criminals get in to user accounts is by so called 'phishing' attacks.
Here are a few things to look out for:
Firstly, the subject line. It is not always easy to tell from the subject line whether the email is legitimate or not.
Check for spelling mistakes - this is a good way to tell if the email was crafted quickly by a scammer
If the subject mentions a bank or another service that you know you don't have an account with, then ignore it
The from address. You will probably have to open the email to check this
If you open the email you will see the actual email address it was sent from. In the example below, you will see that the email was supposedly a speeding ticket from the Greater Manchester Police but the from address was nothing to do with that.
Check any links. If there are any links in the email, hover the mouse over these to display the address they will take you to.
Using the same email as an example, the link to check the 'speed camera evidence' goes to an address that has nothing to do with any police force.
Remember that if the offer sounds too good to be true or if the email contains many spelling mistakes or bad grammar then it is likely to be a hoax.
If in any doubt, ignore it. If a legitimate company needs to get hold of you they will either try again or use a different contact method.