Basically, someone has spoofed your email header to get spam to bounce to you--this is a typical method to get around spam filtering. My guess is your service itself is fine and not compromised.

Your domain may well be in use by spammers though--see spamhaus

en.wikipedia.org/wiki/Spamhaus

and other websites for ways to check to see if your domain is on a watch or block list.

I've been receiving "bounce-back" spam with false headers for years. An email address that I once had that is no longer in a domain that exists was on a home server that was compromised. That created a number of headaches for a friend of mine whose domain it was. However, after applying all the security patches to his unix system, he was able to rid the domain's server of the illegal hacks that had been done to it by remote hackers. It took a lot of work and weeks of frustration to figure out what was going on and to straighten things out...but, as I said, I doubt that's the case with you...unless you physically control your own server...or your ISP has failed to keep its security as patchful as it needs to be.