I see an email addresses sending to your domain that is being blocked because of the server. I am looking into this with the spam service, but it appears this particular google server was sending spam. I will post here when I know more.
Many messages being sent from that server were flagged as spam because the recipients marked them as such. This does not mean that your address was a problem, but the server as a whole was. The flag has been cleared now and you should be ok, unless the server gets flagged again. Preventing that would be up to Google.