Has anyone here (like me) mailed a letter, then RIGHT after mailing the letter forgotten to put on a stamp?

It was a self serve Post Office so there was no one to ask if I could stamp the letter, but I put a note with stamps under the door where the postman picks up the mail and a letter in the letter bin with stamps, both letters gave the name and address of the letter I sent without postage and asked the mailman to simply add the enclosed stamps for me. I also got a number to call early on tomorrow to POSSIBLE get the letter stopped before it's sent out and stamped in time. Oh, did I forget to mention the letter NOT having a return address?

So i'm simply curious if anyone has had this happened and what happened in there situation, or even what you think WILL happen. I'll keep you informed.