Typically these emails will be sent to a list of common first names or departments prefixed to @yours-and-every-one-elses-domain name.
Solution: Under Domains & Email > Domain Name > Email, delete the blank "catch all" email address and specify only the email addresses you use in the forwarding rules area.
They're not accessing your email account at all. Anyone can send an email to anyone using any reply/from address. Very easy to do, go into your email settings and change your reply/from address to anything you want, your email will still send.
When the recipient gets it, they will reply to the reply address in your email. So now this is where spammers come in. They send spam using any old persons email address, because if they use their own, it will be blocked. If they use yours, then less likely to.
It's the content of emails which determine that it is spam. Don't be worried about this happening, it's happening to everyone. So how did they get your specific email address? Ok, consider the other questions on this page.
Solution: Sorry you can't do anything about this.
Probably not, but one of your friends may have. What the viruses do once they've infected any computer is to look at the address book. They will then send emails from everyone to everyone. Since many people have the same friends, then there is no reason that you or the person the email was sent to/from is the infected person. It could be any other person who you both know in common. This error is less likely to occur if you keep your security upto date on your computer, or if you use a web based email program
Solution - If problems persist, talk to your friends who are most likely to forward the most jokes to you. These newby computer users tend to be the ones who don't know which attachments to open or not.