It really depends on the type of bodywork you are getting done AND how much "homework" you are willing to do. I say this as a licensed massage therapist.
I believe that the best possible situation is three-fold - think of the legs of a table. 1-strength training and flexibility 2-massage 3-chiropractic work.
You can go to the chiropractor and get all lined up, but if your muscles are chronically tight, your myofascial restriction will pull your bones right back out of alignment. Likewise, getting a massage can loosen muscles, but if you have weak muscles that are not supporting the body correctly, you will soon be out of alignment again.
What i see in my practice most frequently is called "upper crossed" syndrome where the client presents with a rounded-back, head forward posture....the "computer slump" if you will.
This is so easily remedied and yet it requires a few simple stretches that, surprisingly, many clients aren't willing to do on their own. *laughing* Or maybe not surprising. They'd rather come get their monthly massage. :-)
If you have a therapist skilled in dealing with this situation they ABSOLUTELY CAN help improve your posture. Posture is all about your body's alignment. I've had clients come in to my clinic unable to hold their heads in a straight line - they literally could NOT stand straight! But leave with greater range-of-motion and freedom of movement than they imagined possible. :-)
In the example above a client will present with "burning pain between the shoulder blades" and an inexperienced therapist may focus all their work on the back and shoulders. Not realizing that those muscles are the ones that need to be strengthened! The muscles of the upper neck and chest are the ones that are tight and constricted and need to be loosened.
Anyway - I digress. Yes - massage can greatly help with posture. ESpecially if your poor posture is due to (or has caused) muscle restriction. It's not a cure-all, as others have mentioned, but then, nothing ever is, eh?
Angela <><