We tried all possible email accounts that he thinks it might be but none of them seem to work. Would DreamHost be able to tell us the email associated with a domain he registered? We tried contacting DreamHost but they didn’t answer, going to try again very soon.
We can certainly help your client get the information he/she needs, once we identify their account, and can confirm that they are the account owner. In order to do that, we need to hear from your client? How have you tried contacting DreamHost? I need to know this so I can investigate why you received no reply.
For obvious privacy and security reasons we can’t assist you with this via the forums, but if you, or your client, contact our support staff we will assist with this.
Did you use the contact form Matt suggested to use to reach us? If not, try that, and then let me know when you have sent that message via the form, and I will follow up to make sure you receive a reply and assistance.