To determine the information that should never be emailed, the user should understand the importance of data security and privacy. Email is not a secure method of communication, and any sensitive information sent through email can be intercepted by hackers. Therefore, it is important to avoid sending any confidential information through email.

Option A: Credit card numbers should never be emailed as they are sensitive financial information that can be intercepted by hackers. This can lead to identity theft, unauthorized purchases, and other fraudulent activities.

Option B: Social security numbers are confidential personal information that should never be sent through email. This information can be used for identity theft, fraudulent activities, and other criminal activities.

Option C: Phone numbers are not necessarily confidential information, and they can be shared through email. However, it is important to verify the recipient's identity before sharing any sensitive information with them.

Option D: This option is correct in that any information that is sensitive, confidential, or private should not be sent through email. This includes social security numbers, credit card numbers, addresses, personal information, and any other information that the user would not want shared with unknown parties.

Therefore, the correct answer is:

The Answer is: D