To check and see if there is an infection post in our Malware Infection Removal section following the instruction from Before posting for Malware Removal help. ...WinXP, Vista, Win7, Win8 & Win8.1.
They will be able to assist if there is any security issue and or infection.
To see how full the Drive is
Press the Windows Key and E
This will bring up Windows Explorer
On left side look for This PC and select that
On the right side look under Devices and Drives and look for C: drive and below that is will tell you the size of the amount Free and size of the Drive.
As far as it sending email does this happen in what program and or are you using web based?