The attacks burst back into the spotlight Friday after a biodefense researcher apparently committed suicide as prosecutors prepared to seek an indictment and the death penalty against him for the deadly 2001 attacks, according to officials.
The scientist, Bruce E. Ivins, was a leading military anthrax researcher who worked for the past 35 years at the government's biodefense labs at Fort Detrick, Md.
The bioterrorism attacks forced the closing of two major mail processing plants and contaminated 21 other postal facilities. The Postal Service also had to deal with more than 17,000 hoaxes that disrupted operations nationwide.
Today, more than 1,000 biological detectors are sniffing mail for dangerous contamination at postal centers and other government offices across the country.
Neighborhood boxes to send mail have become scarcer.
Some concerned homeowners switched to outdoor boxes to receive mail instead of using slots in their doors.
More than a million containers of mail to Congress, the White House and other federal agencies have been irradiated to kill potential contamination at a cost of $74.7 million so far. Each container weighs 15 to 20 pounds.
And many packages that used to be dropped in mailboxes now must be handed over the counter to a postal clerk.
"The mail is safer. It's not totally safe but it's safer," William Burrus, president of the American Postal Workers Union, said Friday of the changes over recent years. Two members of his union were among those killed in the attacks.
"There is no guarantee that it won't be repeated at some time in the future," Burrus said. "But postal workers don't focus on it ... they have a feeling of security."
Burrus added that while it has been reported that Ivins would have been indicted, "that is not a conviction. Right now all we have is an accusation."
The post office deployed a fleet of biodetection systems at mail processing locations at a cost of more than $800 million. The annual operating cost has been estimated at more than $100 million.
The detectors check for anthrax and other biological hazards, which officials declined to identify.
Postal workers now are trained to look for suspicious packages and call in postal inspectors if they detect something unusual.