You don't say who you got the email from or what you are supposed to do with the information. From the codes you do have, there does not look like anything needs to change. If your employer got the codes wrong and issues a corrected W-2C, then ask us again.
Here is an explanation of the codes
https://ttlc.intuit.com/turbotax-support/en-us/help-article/taxation/letter-codes-box-12-w-2-mean/L6...
Code C is the taxable cost of group life insurance. This is not entered on your tax return, because that value is already included in your box 1 wages.
Code DD is the cost of employer-sponsored health insurance. This is collected for statistical purposes and has no effect on your tax return either.
Code D is elective deferrals to a pre-tax 401(k) plan. This is not entered on your tax return unless the amount is more than $23,500, or $30,500 if you are over age 50. The contribution was already removed from your box 1 wages, the amount is not normally part of your tax return. (If you have excess contributions, they need to be removed and other adjustments need to be made.)
