Try one of these, it automates the process, ClearProg - Temp File Cleaner or CCleaner - Temp File Cleaner, etc.

Inbound emails are not your problem especially bounced emails don’t open any attachments (could be a tactic to infect you) nor reply to them, the best option is to delete the emails. The likely cause is someone you know with your email address on their address book is infected with a trojan spambot and that uses email addresses from his address book in the from email address. Unfortunately bounced emails get sent to the from address even if that has been faked.

What is your email program ?

Set the Internet Mail provider sensitivity to High, that should be able to identify if your system is sending out multiple identical email.