If the package has any sort of lumpy feel to it, they categorize it as "Hand stamp Only"--which automatically charges you extra. This is what my PO told me when I sent out some ATCs and they came back. If it has one little seed bead on the card, and the postal clerk can feel the bump, that will make it "Hand Stamp Only." I recently had to pay 59 cents for two ATCs (flat even, in sleeves) that came postage due from a swap. You'd be surprised what the PO considers "bumpy".

Yes, there is a 20 cents surcharge for envelopes containing a "rigid object", or "odd sized" (square, or the do not have the address along the long axis).

I always take my ATCs to the counter and ask if the postage is enough. Interestingly, the clerk checks size and weight only... so I wonder if later someone checks for rigidity?

Oh gosh, I'm worried now. I've always just dropped mine into envelopes and put a stamp on them. Not to mention a strip of packaging cardstock to keep things from getting bent. Is there anyway to know if your stuff is going to people with postage due? I'd feel so bad if that was happening.

I had something come the other day with a postage due stamp on it, but it was delivered to my mailbox so I'm not sure how they expected to collect the extra postage on it...? Is there most stuff just sitting at the PO as we speak waiting on me to pick it up and pay the extra postage? How do you know?

So many questions. Sorry. This is a topic I know nothing about.

If it gets spit out by their machines, then it needs to have the extra 20 cents. If it sorts automatically, then it doesn't. My clerks always feel my envelopes. LOL

Usually if your carrier delivers it, you are OK, (and don't legally owe anything). If there was something seriously postage due, you would get a notice to go and pick it up at the post office. You can always reject postage due stuff at the counter if you don't want to pay for it.

If my carrier leaves me something marked postage due, I'll try to leave the change for them the next day. But I don't have a regular carrier, so sometimes they don't pick it up.