1) Some spammer is sending the original messages and using your e-mail
address as the sender.
2) Someone else has a PC infected with a virus and the virus is sending
itself as the original message and using your e-mail address as the
3) The message is the virus itself, pretending to be a returned mail.
4) Your PC is infected with a virus and it has been sending itself. And
this is really a returned mail that your PC sent.
In cases 1, 2, and 3 above, the messages are not coming from your PC and
are not going through your e-mail account. There's nothing you can do
to prevent anyone from sending an e-mail with your e-mail address as the
From header, just as you can't prevent anyone from sending a postal mail
and putting your name and address as the return address. At this point
all you can do is filter out the messages. Your ISP may offer some
filtering at the mail server.
To make sure that case 4 above is not the cause, you should check your
PC with an updated anti-virus program.
Download the malwarebytes from here and install run the full scan