I'm trying to figure out mail forwarding in Germany. So far I understood that Deutsche Post offers for free, and all you have to do is inform them. I would like to ask, if it is possible to to ask them to hold the mail for some time. For example, I am moving to a new state and hence, there would be a time for me without having a place of permenant residence.
If you happen to have a valid new street adress, but aren't physically able to get letters there (lets assume a company is in the process of demolishing the front yard including the mailbox, or you will not actually move your stuff in until the end of the month) you can have the postal system forward your mail to a P.O. Box. This box must be in your name.
As far as I know there is no holding service. The mail will be delivered somewhere, your only choice is the new location.
As an alternative, you can use a "virtual mailbox", a service that will provide you with a (German in your case, but the services are mostly global) physical address for your mail and give you options on what to do with it. One of the most common options is open, scan and send an email to you with a PDF of your letter. Those are private companies unrelated to any postal service and they cost money.