The forwarding order with Deutsche Post only covers letters sent via Deutsche Post. This does not include alternative postal companies.
For our Berlin customers, we are also happy to set up a forwarding order with PIN Mail AG. After registration you will be contacted by us shortly afterwards.
If there are other postal companies active in your region, you are welcome to set up a forwarding order there yourself. How this works is explained in the following article: How can I set up a forwarding order for alternative/regional/local postal companies?