Yes, shipping to Deutsche Post branches within Germany is possible.
Use the following fields in the address field of the registration form for post office and post number:
In the fields "Street" and "Number" write "Postfiliale" and the number of post office.
Example
Field Street: Postfiliale
Field number: 123
Please write your postal number in the field "address supplement".
Example
Address suffix: 1234567
Your finished postal branch address will look like this
John Doe
Postfiliale 123
1234567
22222 Sample city