Your domain is not necessarily being accused of e-mail spam. Here are the categories from their FAQ:
- spam domain
- phish domain
- malware domain
- botnet C&C domain
- abused legit spam
- abused spammed redirector domain
- abused legit phish
- abused legit malware
- abused legit botnet C&C
I would suggest checking your domain name and the IP address of your domain name and MX record at http://mxtoolbox.com/blacklists.aspx and making sure you are not listed in other blacklists that you are unaware of. If all is clear, then it likely has to do with the server configuration.
Keep in mind that for many blacklists, if you are on a shared server, it may be another site that you can potentially be associated with. This would mean that you are at the mercy of the other site. But that may not be the case here.
I would double check the version of WordPress is free from vulnerabilities including any plug-ins, extensions, and themes. I would also check the various versions of other software including your storefront, e-mail SMTP server, FTP, and so on. Make sure that your site has not been compromised and you are not aware of it. As well, there may be system services that are open via your hosts build procedures and operational processes that you are unaware of and would normally have no control over. Check these if they exist.
You can check out this part of the FAQ and follow some of the links to see if there are any clues: http://www.spamhaus.org/faq/section/Spamhaus%20DBL#421
The bottom line is this:
- Your site has a vulnerability that is easily detected...
- Your site is engaged in an activity that you are not aware of...
...that is either easily detected by a scan or continues to retrigger the blacklist. Keep in mind that this blacklist if fully automated and as they seem to indicate will remove any record immediately without question, however, if the problem persists, the the domain name will be relisted. This is an important point to consider. Keep working to find the problem until you are cleared and stay clear.
Since SpamHaus is not particularly helpful, I would suggest paying attention to any return code if you were to query their blacklist as that would help identify the area you need to look into. The codes are listed here along with some explanation: http://www.spamhaus.org/faq/section/Spamhaus%20DBL
You may find that http://mxtoolbox.com/blacklists.aspx may give some clues that SpamHaus is not. You can check your domain name there as well as your specific IP address.
On a side note, some odd little webhosts use IP address lease or rotation schemes and sit behind a generic PTR record that points to a domain name like hosted.example.com. I am not saying that all sites that sit behind a reversed domain name like hosted.example.com are a problem, but that could be an indication.
Make sure you have a dedicated and clear IP address and that you are on a dedicated server if possible. Also make sure that the PTR record resolves to your domain name if that is possible. Check the basics first. It could be as simple as this.