Beware, if you send to most US recipients, we get bundles of junk mail (including postcard junk) multiple times every week. These might be thrown in the trash with the junk mail by accident and you might get complaints for non-delivery if people seriously want the recipient to see them.
Huh, where do you live that this happens? In CT, my mail is not bundled at all, so I glance at each item before I throw it away. Also I would think that the bundled items would be shipped bulk-mail rate, but these cards are shipped standard first class postage so shouldn't be bundled in with the junk. These postcards should be just like if you were on vacation and threw a stamp on a postcard you bought in a gift shop.
Thanks for the heads up though!