The part about letters from parties is probably mostly relevant to German citizens, though non-German citizens living in Germany might still be affected by parts of these laws.
Did you also receive letters from parties in the last weeks and wondered how they go your address? According to §50 Absatz 1 BMG parties may ask for your name and full address prior to an election.
This also applies to editors of address-books, public religious institutions and even the Bundeswehr!
You're living in Magdeburg and don't want your address to be spread everywhere?
Then you can easily go to the form-pool on magdeburg.de and fill out the form "Widerspruch gegen die Erteilung von Melderegisterauskünften (klick!) and send it signed to email@example.com. Alternatively you can also post it to the city (we tested both variants for you).
If you're not living in Magdeburg, you can search for "Antrag Übermittlungssperre" for your place of residence and you should find an equivalent form. If you don't find one right away you can also send a generic form, which isn't specific for your residence. You might to have send it via post that way.