ST. LOUIS -- For decades, an idiosyncrasy in the mail delivery system has forced some rural northern Missouri residents to have Iowa mailing addresses, which has created roadblocks and red tape for residents when they vote or pay taxes -- even when they die.

Local officials have been asking for help for years from local politicians and postal officials to no avail. U.S. Sen. Claire McCaskill recently learned about the quirk, calling it "one of the dumbest things I've come across."

McCaskill, a Missouri Democrat, sent a letter last week to Postmaster General Megan J. Brennan, asking the U.S. Postal Service "take immediate action" on behalf of Missouri residents who have Iowa mailing addresses. Brennan's spokesman David Partenheimer said in a statement last week his agency is "working with the senator to address this issue and will respond directly to her office." He declined further comment.

The exact number of affected residents is unknown, though one county has more than two dozen misaddressed residents. Also unclear is why Missouri residents were assigned Iowa postal addresses in the first place. McCaskill's letter said it appears to have something to do with mail delivery routes along the sparsely populated area where the two states come together, though local residents never were given a good explanation.

In Missouri's Clark County, some residents launched a petition drive this summer to get address changes because the county of 6,700 residents is adopting a new 911 system and accurate addresses are crucial, said Jena Church, the county clerk.

The quirk also makes voter registration difficult because Iowa addresses aren't recognized in Missouri's voting system.

"We always put their address as the courthouse address," Church said of the 30 or so Clark County residents with Iowa addresses. "It has to be a Missouri address to have a voting district."

In other cases, residents have been required to file provisional ballots, Church said.

Problems extend to other areas, too. Church said the address issue can create a headache in filing taxes: Several of the affected Missouri residents have been told by the state of Iowa they should be filing returns to Iowa because of their addresses. The two-state confusion also can slow the process of obtaining a death certificate and even make it more difficult to collect life insurance after a relative has died, Church said.

McCaskill asked Brennan to provide her with a history of the issue, including the year Iowa addresses were assigned to Missouri residents. She also asked for a dedicated Postal Service employee to be appointed to resolve the problem and work with residents who have Iowa addresses but live in the Missouri counties of Atchison, Mercer, Putnam, Schuyler, Scotland and Clark.

"The notion that Missouri residents have faced numerous hassles for decades because they have an Iowa mailing address is one of the dumbest things I've come across," McCaskill said. "This needs to get fixed, and I plan on doing everything I can to help."