my email account is sending spam emails to address that aren’t even in my contacts

The other day I received 36 'Delivery Status Notifications (Failure)' reports. None of the reports were for emails that I had sent and they were all mostly to aol accounts, but none to any of the accounts that were in my contacts list. All the emails were also in my sent items folder. All the emails had attachments, none of which I opened, and all were had watches in the headers. Has my account been hacked? I have changed my password to a more secure one now. Do I need to do anything else?

Andy