If IMDB have been unable to verify a credit. How do I go about giving them the Producer's email address?

You can contact an IMDb representative in private through the IMDB Contact Us form (Link: https://help.imdb.com/contact). Please provide the 18-digit reference number of the submission. Please note that I'm not sure providing the producer's email address will be enough proof to verify credit. 

Click the following buttons/drop-down menu items on the form.

IMDb Fan/Contributor Questions -> Filmography Credits -> Provide Credit Evidence -> Email

You'll receive a response from an IMDb representative within 24 hours via email.

Hi Teresa -

Just adding onto the information GMJ provided above, you can find additional information on providing evidence to verify a credit on the following Help page:  https://help.imdb.com/article/contribution/contribution-information/how-can-i-submit-additional-veri...#

Let us know if you have any questions!