If you notice bounce messages for mail that appears to have came from the email account for your site or a reply to a message you never sent, you may be the victim of a spoofing attack. A spoofing attack is when someone fakes the return address on outgoing mail to hide the true origin of the message.
As a precaution, you should:
1. Scan your computer for any viruses, etc., and make sure your computer software is up-to-date
2. Login to your cpanel http://SITENAME.COM/cpanel/ OR cpanel.SITENAME.COM and change the password for the email account in question
Helpful Links:
cPanel User Documentation
https://documentation.cpanel.net/display/ALD/cPanel+User+Documentation
cPanel Tutorials
https://www.youtube.com/playlist?list=PLZk46idJS6s54hAX8K79_AY8brgBwPtHd
cPanel & WHM Documentation (Dedicated Server Clients & Resellers)
https://documentation.cpanel.net
WebHost Manager - WHM User Guide (Dedicated Server Clients & Resellers)
https://documentation.cpanel.net/pages/viewpage.action?pageId=1507786
