Every day the US Postal Service processes and delivers half a billion pieces of mail each day. 

That’s an average of 351,656 mailpieces processed each minute. Fast!

Not surprising to learn that letters or postcards can get damaged in the process. Sometimes, you may even see a rub or smear on postcards that look similar to the example below. 

In this post, you’re going to get the behind-the-scenes view of an actual USPS processing plant as we examine what really causes smears and rubs to postcards. 









Smears rarely occur during the print process.
At first glance, you might think the postcards were mailed wet or smeared during the printing process, but this isn’t the case because in the Click2Mail print shop we don’t even use ink. We use toner crystals

CMYK Toner Powder

These electrically charged carbon crystals actually fuse to the paper with heat, bonding to the paper in milliseconds. The printing is dry before the postcards are cut into individual mailpieces. 


<= Example of toner crystals


After the postcards are printed, they’re systematically checked for quality and any anomalies are removed. 

So if smears and smudges aren’t happening during the printing process, then where? 


To find out how and when damage happens, we took a field trip to a local USPS plant.

Here’s what we learned.

To get a better understanding, we connected with the USPS Processing and Distribution Center (P&DC) in Denver, Colorado. We worked with one of their team of engineers and managers to test our letter mail, postcards, and flyers on the equipment. Here’s what we found. 

The Delivery Bar Code Sorter (DBCS) is really the workhorse in a mail processing plant. It’s capable of processing about 40,000 pieces of mail an hour. The machine is programmed to sort the mail into the appropriate bin out of 270 bins.

This is the DBCS “letter feeder” with covering removed. The mail is placed on the “jogger shelf” to the right where the mail is jogged to tap it down so that it can enter the feeder. The DBCS’ Optical Character Readers (OCR) reads the address then sorts it to the individual bins. (see above)

Depending on how far the mail has to travel, it may be processed by four to six different DBCS machines along the way to its final destination (local post office). These sorting machines are made up of a series of belts and rollers that sort the mail based on outgoing ZIP codes. 

The green and black rubber belts and rollers are typically the culprits and are usually the reason why you might see color smudges or scuffing on your postcards. The rollers physically grip and contact the mailpiece as it pushes (sorts) it through to the correct ZIP code bin.




If the roller applies too much pressure as it grips the mail, it may penetrate the color toner and UV coating on the surface of the postcard, leaving scuff marks. 

Occasionally, the equipment may even rip the cards. Usually, though these marks occur about halfway to three-quarters of the way down on either side of the card where the high-speed belts make contact, like the example below.



Why first class returned pieces are almost always damaged

When first class mailpieces are undeliverable — that is, when you see pieces with a yellow “nixie” sticker from the carrier indicating why it was not deliverable and returned — they become especially vulnerable to scuffing and marking. Because the USPS takes extra steps to attempt to deliver this class of mail, the postal pieces are intentionally sent through the DBCS sorters several additional times to ensure that they are in fact “undeliverable”. 

Next time your first class undeliverable postcards return to you, take note how scuffed they may look. This is because it’s going through the sorting machines more often than other pieces, increasing the chances of it getting caught or snagged.




But what causes the ink to melt? 

At the top of the sortation bins, a black belt causes enough friction to rub and smear the toner off the paper. 

(Top of the sortation bin and black belt)

In the photo to the right, you can see us exaggerating the pressure of the postcard on the black belt and we were able to reproduce the smear – every time!  

How to reduce the risk of damage to your mailpieces
We tested different paperweights on the postcards and learned that heavier weight didn’t prevent the problem and in fact, in most cases, it caused more tears in the postcards.

For just a few cents more choose UV coating (versus uncoated stock) will help to make your images and colors stand out and should help to reduce postal scuff marks. 

We changed our flyers/selfmailer and have added another tab to the lead edge to the mailpiece.  That should help them from getting folded or bent in processing.

Next time you receive a postcard that looks smudged or smeared, don’t worry. It happens rarely. The postal service is doing their best to deliver those half a billion pieces every day in the most reliable way.

Lastly, HUGE thanks to our partners at the USPS Denver P&DC Plant Manager, Manager of In-Plant Support, Maintenance Tech and DBCS crew who accommodated our request to test on the equipment. Their time and expertise was incredibly helpful in diagnosing this issue.