You need to talk to your Post Master so as to educate yourself. From what you stated, and from my own experience on the road, these are a few things I learned.
Magazines do not get forward unless you pay for premium service. Holding of mail is good for up to a month. If the envelope has the code on it for "do not forward" (i.e. that check) it will be sent back to the sender. Takes 1-2 weeks before you'll get mail at the new address. They seem to bundle it in the beginning.
Best to talk to the Post Master who knows the system better then me.