One of the hazards of old and vintage postcards is that they sometimes smell from being stored or occasionally from cigarette smoke. A lot I purchased from e-bay had this issue, and I wasn't sure what I was going to do. I didn't want the smell to contaminate my other cards, nor did I want to send stinky cards to trading partners.
I looked online, and one suggestions was to put two or three postcards on a baking sheet and leave outside in the sun. I might have done this in Phoenix, but in Ithaca, where it is humid and likely to rain, it didn't seem like a sound plan. Additionally, it would have taken forever working on just two or three cards at a time.
Next, I tried putting a dryer sheet in the plastic bin with the postcards. That seemed to help a little, but it primarily masked the musty scent rather than removing it. On George's suggestion, I put baking soda in a small open container and then put that in the plastic bin. Not too much luck there. I thought maybe the baking soda needed more opportunity to breathe, so I placed in in tea filters (what you buy in the grocery store for loose tea). That helped, but too slow for my taste. My last and current attempt had me putting baby powder in the tea filter. The powder particles are smaller than the holes in the filter, so I double-filtered it. This seems to be working fairly well.
Have you had this problem? What have you tried and how were the results?