Investigate Email Account Breach

Unrecognised emails have just gone out from my personal mailbox without my consent. A draft appeared on its own with 401 addresses in CC plus an attachment and, the moment I opened the mailbox, the message was fired off automatically... (Budget: ₹100 - ₹400 INR, Jobs: Computer Security, Digital Forensics, Internet Security, Linux, Network Security, Penetration Testing, Security, Web Security)