As a mailcarrier I am surprised your mail was returned to you. I can't tell you how many times I have used my own money to help someone out with postage in your situation. I myself have sent mail to credit card companies with short postage. Most of the time, especially during a recent postage rise, the companies you are sending checks to want their money and will absorb the postage. I believe the rule is that if you send something short of postage it is still delivered and it is left to the recipient to pay the postage due. Everyday I work I pay the postage due items that I am delivering to the recipients and they in turn reimburse me. Sometimes I get stiffed. I also have the option of going to their door and requesting the postage due. The recipient has the option to refuse and the mail is then returned to the sender.