Run a full scan with your anti-virus software.
Then download, install and run the free version of Malwarebytes Anti-Malware:
https://www.malwarebytes.org/antimalware/
(NB: When installing it take care to deselect the pre-ticked option to take a free trial of the Premium version).
Then use System Restore to take your computer's registry back to the most recent available date prior to opening the dodgy email. (Start > All Programs > Accessories > System Tools > System Restore).