USPS Hacking (Autumn, 1991) --------------------------- By The Devil's Advocate The U.S. Postal Service (USPS) is just like any other system. It is huge and complicated, with lots of acronyms and technical jargon. It is riddled with inconsistencies, and is prone to human error. Most importantly, it beckons to be explored by that very same bunch who are so fond of creative exploration: Hackers! POSTNET The Postal Numeric Encoding Technique (POSTNET) is a bar code system initiated in 1983 to help accelerate the sorting of letter mail by automated equipment. The term "POSTNET" refers to a bar code, which represents either a five digit ZIP code, or a nine digit ZIP+4 code. POSTNET is most often preprinted on business or courtesy reply mail by businesses. POSTNET can also be jet sprayed on envelopes that are processed by an Optical Character Reader (OCR) machine. POSTNET consists of a combination of 22 long bars and 30 short bars. The 52 bars encode a nine digit ZIP+4 code plus a checksum number. Learning to read POSTNET is easy for anyone familiar with binary. The first and last bars (always long) are guide bars, and play no part in determining the encoded ZIP+4. Each group of five bars after the first guide bar represents one ZIP+4 number. The group consists of a combination of two long bars and three short bars. The position in the group has a corresponding value. The values from left to right are 7-4-2-1-0. A ZIP+4 number is obtained by adding the values of the positions containing the two long bars. The only special case is when the added values equal eleven. In this case, the number represented is zero. POSTNET also includes a checksum number at the end for the purpose of error detection. You can determine what the checksum number should be by adding the numbers of your ZIP+4. The last digit of the resulting sum, when subtracted from 10, will yield the checksum number. For instance, if your ZIP+4 is 11953-0752, then the sum is 1+1+9+5+3+0+7+5+2=33, the last digit of the sum is 3, and the checksum is 10-3=7. The USPS encourages companies to preprint the ZIP+4 POSTNET on business reply mail by offering reduced postage rates. The advantage of using POSTNET is not only in savings but in speed. Letter mail that uses POSTNET is processed faster and more accurately than mail that does not use POSTNET. MARK The MARK facer-canceller serves three purposes: 1. It cancels and postmarks letter mail. 2. It arranges letters so that they all face in the same direction. 3. It separates POSTNET letter mail from mail that does not use POSTNET. The MARK utilizes fluorescent and phosphorescent detectors that enable it to detect the presence of minute traces of phosphor on stamps, prestamped postcards or envelopes, and meter marks. The MARK is also capable of detecting preprinted Facing Identification Marks (FIM). FIM Open any magazine and you will find business reply mail cards inside. Nearly every card will contain a FIM. These six-line bar codes are much taller than POSTNET, but not nearly as wide. They are located at the top of the card, just left of the postage area. The MARK recognizes four types of FIMS: FIM A five vertical lines (2,1,2) Letter uses POSTNET and needs postage. Used for courtesy reply mail. FIM B six vertical lines (1,2,2,1) Letter does not use POSTNET and does not need postage. Used for business reply mail. FIM C six vertical lines (2,1,1,2) Letter uses POSTNET and does not need postage. Used for business reply mail. FIM D seven vertical lines (3,1,3) Letter does not use POSTNET, needs postage, and is OCR readable. Used for courtesy reply window envelopes. Business reply mail that uses FIM B or FIM C (indicating that no postage is necessary) must also use horizontal bars to indicate that USPS must collect postage from the business to which the mail is addressed. The horizontal bars are located on the right hand side of the cards and allow clerks to easily spot these cards in a tray full of other letters. The MARK first checks to see that a letter has postage (stamp, meter mark, or FIM). After passing this test, the letter is then canceled, postmarked, and directed to one of eight bins based upon the orientation of the letter and the presence of POSTNET. Four of the eight bins are for POSTNET letter mail, while the other four bins are for mail that does not use POSTNET. Each group of four bins accepts letters according to their orientation. Because letters can enter the machine right side up, upside down, backwards, or forwards, the MARK must have a bin for every possible orientation. The MARK also utilizes a ninth bin for letters that are rejected by the machine for lack of postage. For example, if a letter does not have postage, and the letter does not have FIM B or FIM C (indicating that no postage is necessary), then the letter will end up in the reject bin. Sometimes letters that do have legitimate postage may end up in the reject bin. If a stamp is not placed in the upper right hand corner of an envelope, then the MARK's sensors may not detect the phosphor, and the letter will be rejected. A clerk manually goes over all of the rejected letters individually to determine why they were not processed. LSM The Letter Sorting Machine (LSM) was first used by the USPS in the late 1950s. The huge semiautomatic beast requires a group of operators to sit in front of twelve consoles while letters are zipping by at a rate of one per second. The machine automatically positions a letter in front of an operator, who then has one second to key in the first three digits of the ZIP code. The letter is then whisked away to one of several hundred bins according to the keys that were depressed. If an operator fails to key in anything then the letter will go to a reject bin and will eventually be fed back into the LSM. If an operator happens to key in the wrong code, then a slight possibility exists that the misguided letter will be caught by a clerk before it is shipped. Otherwise, the letter will be delivered to that location, wherever it may be, and will eventually be delivered back again. LSM places a marker on the back of every letter that is processed. The marker consists of two alphanumeric symbols. The first symbol is always a letter ranging from A to Z. The second symbol is either a letter ranging from A to C, or a number ranging from 1 to 9. The marker can therefore be one of 319 possibilities. The marker may also be one of several different colors, although the color does not indicate any useful information. According to USPS LSM operators, the marker indicates which console processed the letter. However, this information is fairly useless because we still do not know which specific LSM processed the letter. The USPS uses hundreds of LSMs nationwide, and each of those LSMs has twelve consoles. I am uncertain how to translate a specific marker into a specific console, nor do I understand why the marker can be one of 319 possibilities if there are only twelve consoles. BCS The Bar Code Sorter (BCS) processes POSTNET letter mail. The BCS is therefore limited to sorting only business reply mail and other high volume mail that incorporates the POSTNET. At a sorting rate of ten letters per second, the BCS is considered slightly faster than your average clerk. The letters must be properly positioned and fed into the machine manually by an operator. This is accomplished by stacking trays of letters received from the MARK onto a feeder unit. The operator does not have to properly position each letter because the letters received from the MARK are already facing the same way. MLOCR The Multiline Optical Character Reader (MLOCR) is the latest and most advanced machine in the USPS letter sorting arsenal. This million-dollar monster is capable of reading all of the lines that comprise a letter s address. It then takes this information and compares it against its own internally stored address directory. Finally, an appropriate POSTNET is jet sprayed on the letter so that it can be further processed by a BCS. The purpose of the MLOCR is therefore to spray POSTNET on letters that do not use POSTNET, so that they can be processed by a BCS. The advantage of the MLOCR is that it can determine an address even if parts of the address are illegible, incorrect, or missing. For instance, if someone forgets to include a ZIP code, or uses the wrong ZIP code by mistake, then the MLOCR can still determine the correct ZIP code by comparing the street, city, and state with its own address directory. It will then spray the letter with the correct ZIP+4 code (the MLOCR will always try to spray the letter with a ZIP+4, even if the letter uses a five digit ZIP code). Early OCRs could only read type or clearly printed handwriting. In the near future, however, the MLOCR will recognize script as well. The MLOCR is capable of reading the address even if it is skewed (i.e., printed at an angle). The MLOCR does not have the capability of knowing whether or not a letter already has POSTNET, nor can it sort mail according to POSTNET. Therefore, it is possible to receive a letter that has two overlapping POSTNET bar codes. Like the BCS, the MLOCR only accepts trays of properly positioned machinable letters that must be fed into the machine manually by an operator. Mail Hacks There are at least three things that everyone familiar with the USPS would like to do: 1) Mail letters for free; 2) Get their letters delivered quicker; 3) Find out why it takes so long for their letters to arrive. Free Mail It is not difficult for someone to mail a letter for free. It is, however, extremely difficult to mail many letters for free. The USPS is always looking out for mail fraud, and has an entire agency devoted to just this task. Even if a good mail hack works once, it is not likely to work if used repeatedly. Therefore, if you are reading this article with the intent of saving money by tricking the USPS and mailing letters for free, then you would do better to give up now before you are busted. Of course, anyone with even the slightest iota of curiosity would want to know some of the methods. Perhaps one of the oldest scams in the book is to switch the destination address with the return address and mail the letter without postage. The USPS will then return the letter to its "sender" for postage. Of course, the USPS is not that stupid, and this trick rarely works for nonlocal mail. A much better mail hack would be to use a laser printer to print a FIM B on an envelope. The MARK will then treat this letter like a business reply mail card, and will not reject it for lack of postage. Of course, the problem with this technique is that a mail carrier will almost certainly notice the missing postage before the letter even gets to a MARK. Therefore, you would have to bundle this letter with another letter that has postage, place the letter with postage on top of the illegitimate letter, and use a rubber band to bundle them together. The mail carrier will not disturb this bundle. Eventually, the bundle will reach a General Mail Facility (GMF) where clerks quickly separate bundles on a conveyer belt. It is extremely unlikely that they will notice the illegitimate letter at this point. From the conveyor belt, the letter will journey to the MARK. Once the MARK processes the letter, it is unlikely that anyone will notice the missing postage until the letter reaches its destination. The final obstacle is the mail carrier who will physically deliver the letter to its destination. At this point, the letter is postmarked, so one can only hope that the mail carrier is not too nosy. Fast Mail Getting your letters mailed quickly is a much better hack than trying to mail your letters for free. Not only is it legal but the results are guaranteed. Normally, a letter reaches a MARK where it is processed and sent to an MLOCR. If the address on the envelope is readable by the MLOCR, then it is jet sprayed with a POSTNET and sent to a BCS. Otherwise, the letter is rejected and sent to an LSM. The one thing you really want to avoid is having your letter processed by an LSM. The operators who run these machines are notorious for keying in the wrong code, causing your letter to journey out of its way to strange and exotic parts of the country. Never write the address on your envelope in script unless you want to delay your letter. One way you can get your letters processed quicker is to have your letters skip some of the steps in the sorting process. The method involves using a laser printer to print a FIM A and a POSTNET on an envelope. The FIM A will instruct the MARK to treat the envelope as courtesy reply mail. The MARK will look for postage, which you have thoughtfully provided, and then send the letter into a bin with all of the other POSTNET mail. This mail will then be placed in a tray and sent directly to a BCS, skipping the MLOCR and completely avoiding the LSM. By using POSTNET, you are taking advantage of the same multimillion dollar equipment that is used by businesses. Another advantage to using this method is that your letter will be processed entirely by machines. From the moment your letter enters the MARK until the moment it leaves the BCS, no clerk will see your letter. In addition, the USPS will be pleased with your creative use of their multimillion dollar machinery. Snail Mail Now that you know what happens to your letter when you mail it, you can use this information to determine why it takes so long for your own mail to arrive. The next time a letter comes in the mail, analyze it for telltale USPS markings that may give you insight into how the letter was processed. If the letter has POSTNET on it, then you know that the letter was processed by an MLOCR and a BCS. You can then read the POSTNET to make sure that it represents your ZIP code. If the POSTNET is incorrect then that would certainly explain why your letter was delayed. You should also flip the letter over and look for LSM markers. You should not see any more than one or two markings. If the back of your letter is covered with them, then you know that your letter probably had quite a journey, whipping back and forth around the country before it reached you. Keep in mind that it is not unusual for a letter to be processed by both a BCS and an LSM. Not all GMFs use the same machinery, and the average clerk can screw up any letter, even if it is processed by machines.