Email spoofing is the creation of email messages with a forged sender address – something which is simple to do because the core protocols do no authentication. Mail gets sent from user email address though user have not sent any mails through that email-id, this process is termed as “Spoofing”. Email spoofing is the practice of changing your name in email headers so that it looks like the email came from somewhere or someone else.
A. This is possible if some one is using your email id for reply address which can be done with the help of some script or any other way and send emails to random addresses, those might be not exist at all,so you can`t do anything for this situation.
B. But if some one is sending the emails by logging into your email accounts to those email addresses (which is a very rare case),the best approach is to change the passwords of your email accounts by assigining the passwords which are not easy to be guessed so as to avoid any further invalid access to your email accounts.
C. Another possibility of receiving spoofed emails can be due to virus emails, however solution to this is to keep scanning the mails you receive and site data regularly using virus scan feature available in your control panel.