Excellent video by Tom Scott on what happens with unreadable mail. These are envelopes where the mailing address cannot be read by the automatic processing of local USPS facilities.
Basic Process
- Local Processing Plant automatic processing. Something is unreadable.
- A picture of the unreadable mail gets sent to the remote encoding center
- If it is read in time then the piece of mail is able to stay “within automation” at the local processing plant. If it isn’t read in time then there is a second chance when it is sent through the local processing plant again a couple of hours later.
- The guessed address is compared to the known address database. If there is only one matching address then that is that. If there are multiple similar addresses, then one needs to be selected from the matches from the database.
In the past there have been more of these encoding centers. But over time the trends are that fewer people are addressing their mail by hand and that the automatic processing technology is becoming better and better.
More information on USPS history and envelope history here.