Theoretically nothing. An email address is not a secret information per se, and there is nothing much a hacker do than what you have given permission to.
In practice it depends on how you use it :
- If it is strictly an email address, i.e. a way to send you a message then you only need to have a good password
- If it includes extra information (e.g email@example.com firstname.lastname@example.org) then you released some information. Another example is a work email. It automatically reveals your company name. Example, email@example.com. This gives a clear signal that the owner of this email works at Ken City Media
- If it is your login on websites then, well, someone knows your login by knowing your email.
- With email, someone can start Social Engineering that targets you. To simply put, Social Engineering means 419 (azar, adwen k3se3). Take for example,if your email contains other info as stated above(firstname.lastname@example.org), someone can easily draft this message to minister of information. “Good morning, this is Kaunda from the presidency, I can’t access my official email, I’v forgotten the password. Kindly resend the Kelni/GVG contact to email@example.com asap, so that I can have a fair idea of how to argue it. I’m meeting my father 9am this morning. Will do all my best to convince him it isn’t a bad deal at all. Just relax“.
All he can basically do with just your email is Social Engineering (or Spamming). Whether the hacker wins or not depends on what you do when the mail lands in your inbox.
The advice is always simple
Do not open mail attachments you are not expecting.
All in all this is not a big deal if your accounts have good passwords and you also apply common sense. Again : Email is supposed to be public (or at least non – confidential) information.