Since the EU General Data Protection Regulation (GDPR) became effective in May 2018, DENIC no longer records an administrative contact (Admin-C) for reasons of data economy. Consequently, no contact data is available.
According to item VI of the DENIC Domain Guidelines, the domain holder is obliged to provide accurate and complete data - including an e-mail address - with the domain request.
If this obligation is not fulfilled, you as the domain holder risk the loss of your domain, as incorrect or missing data entitle DENIC to terminate the domain contract without notice. This also applies to the TRANSIT process, if no valid e-mail address has been stored that can be used for the communication between you as the domain holder and DENIC.
For storing your correct e-mail address, please contact your current provider or, if the domain is undergoing the TRANSIT process, your future provider or DENIC directly.