On October 21, Democratic candidate Dan Seals' congressional campaign dropped off 8,200 pieces of mail at the post office.  As is customary with political materials, the campaign had sleeved and red-tagged the delivery, which was subsequently transferred to a distribution facility in Palatine.  About a week later, they realized that the mail hadn't hit any mailboxes in the 10th District and made repeated calls to the post office.  On Wednesday, October 29, they learned what had happened.  From an email sent to Seals supporters today:

After realizing that supporters had not received the letter, we discovered that the mail had been set aside and out of sight at the post office. The letters were supposed to have been treated as first class mail. They were not.

Very strange. The sleeves and red tags had also been removed, according to the campaign.  More from the email:

Authorities are now investigating the situation, but we have already missed a critical opportunity to raise funds and keep Dan on the air in the final days of our campaign.