SYMPTOMS OF A POSSIBLE COMPROMISED EMAIL ADDRESS INCLUDE:
Complaints about spam being sent from your email address.
You are not receiving any email.
You appear to be missing email.
You are receiving large numbers of undeliverable or bounce messages you did not send.
You are not able to log in to your email account.
Unknown email appearing in Sent Items folder.
IF YOU SUSPECT THAT YOUR MAILBOX MIGHT HAVE BEEN HACKED:
Make sure your PC is current with OS updates and anti-virus/malware software.
Depending on how your account has been abused, you might have to contact everyone spammed by your hacked e-mail to advise them that the communications were not legitimate.
Set up several e-mail addresses. Use your original e-mail address for personal or business communication as you’d normally do. Then another e-mail address to communicate with your service provider, since many now ask for an alternative address as added protection. Then, use a totally separate e-mail address only for registering for sites, newsletters, online shopping and other services. In this way, the risk of a possible compromise is spread.
Use different and strong passwords for each account - one that is at least six characters long, and is a combination of letters, numbers and capitals/lowercase.
On a secure PC, log into your e-mail and then check whether or not any of the settings have been changed by a hacker. If any of the settings have been altered, delete the new settings.
Once you have changed the settings, create a new password, and add your secondary e-mail account as your alternative address.