Currently Being ModeratedJun 20, 2012 1:00 PM (in response to banrock)
Unless you can see those emails somewhere in a "sent items" folder, they're probably not coming from you but rather from someone else, most likely someone who had your email address in their address book and contracted an email virus. Said virus picked your address out randomly and sent out the messages with that as a fake "sender". If that's the case, then other than warning everyone you know that their system may have a virus, there's nothing you can do.
If you do see such sent emails in your account, then most likely either your email account has been hijacked or your computer has been compromised, most likely with a virus or worm.
Currently Being ModeratedJun 20, 2012 2:46 PM (in response to banrock)
It would be a computer that would have been compromised, not on a iOS device. There are many Windows email viruses that can hijack someone's address book and blast out spam messages, often with the virus attached.