As emails were in your 'sent' folder you must have had account hacked.
Change your password (make sure that the email address that in your details is the correct one for them to send the reset info to, or you won't be able to reset, I think you have to have it sent to a different email address) and devise a 'secret word' to add to your email subject header so that your contacts will know if an email is from you or from unmentionable git or a spammer. Their email addresses are prob now on a spammers list (who will spoof your email address so that emails appear to have come from your account - but will not appear in your sent folder as they are not actually sent from your account).
Another option is you could use a different email address for a while.
These things happen, don't let it get to you.