If your account has a dedicated IP address this means that all mail from this IP address came from your account specifically, not from any other WestHost client. In other words, it is indeed mail that you've sent that has caused your IP address to be blocked. You'll need to work with the particular company that has blacklisted you to find out specifics on why you are listed and what you can do to get removed.
Large email providers maintain their own blacklists based on spam reports from their users and statistical modeling tools. In other words, email users of this company have specifically identified messages sent through your WestHost account as spam, or your WestHost account is exhibiting behavior characteristic of a spammer (e.g., sending too many e-mails). Listed below are some typical reasons that cause IP addresses to be blacklisted, but again, you'll need to contact the particular company that has blacklisted you to find out specifics for your case.
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1) Forwarding spam counts as sending spam. If you are forwarding mail from your domain to a personal e-mail account, you should switch to remote POP fetching instead of using forwarding (if your personal e-mail account supports this feature). Comcast, Gmail, Hotmail, OptOnline, SBC Global, Yahoo, and many other email providers all allow you to fetch mail from other POP accounts. Instead of forwarding mail from WestHost to Yahoo and getting blacklisted for forwarding spam, for example, you can disable forwarding at WestHost and configure Yahoo's "Mail Accounts" setting to fetch the messages.
3) If you send newsletters or other mass mailings, be aware that US federal and state laws limit commercial e-mailing. For instance, the Federal Trade Commission may impose fines of up to $16,000 PER RECIPIENT for e-mail messages that violate the CAN SPAM Act. The Act requires that your mailings include a valid physical postal address, do not use deceptive subject lines or e-mail headers, and provide a working opt-out method. Please refer to the Federal Trade Commission for more information: http://www.ftc.gov/bcp/edu/pubs/business/ecommerce/bus61.shtm
4) Lastly, your WestHost IP address can become blacklisted if someone has gained access to your mail server and is using it to send spam through your account. Ensure that your cPanel and e-mail accounts are using strong passwords. I would recommend changing the passwords for your cPanel and all of your user accounts now. Password should contain uppercase and lowercase letters, numbers, and symbols and should not be a word in the dictionary. Also check any scripts or programs on your website that have the ability to send e-mail (blogs, bulletin boards, contact forms, etc.) for security vulnerabilities that would allow unauthorized mail to be sent. Make sure you are using the latest versions of these scripts and programs. Also make sure the administration areas for these scripts and programs are protected with strong passwords.