How to receive mail from companies?

I know you can sign up for online newsletters etc that come in email form, but I want to be able to give my favourite companies my mail details online so that I receive newsletters and promotions etc. through the post. Most of the websites say 'contact us' which doesn't include being contacted back through the post, and on one I was able to 'register' which included putting in my address, although I don't know if I will ever be sent mail through the post by them.



So basically I was wondering does anyone know the best way to get on the mailing list of a company ?



Would I have to write them a letter or can I do it online somehow?



Many Thanks

Many Thanks

idk............