Even a letter to Santa Claus can no longer be considered safe.

The US Postal Service (USPS) warns that its usual appearance - clumpy with hay for Santa's reindeers, or, worse yet, cookies that leave grease stains on the envelope - fit the description of mail that should put Americans on notice this holiday season. The penmanship is often childlike, and sometimes there is no return address.

Following the recent deaths from anthrax spread through the mail, the USPS is asking the public to be alert through what is traditionally the busiest mailing period of the year: the weeks between Thanksgiving and Christmas.

Last year, the USPS handled 2bn pieces of mail during this period. It expects to be even busier this year.

"Traditionally, people communicate more with friends and families in times of stress," says Mark Saunders of the USPS. He warns those on the receiving end not to be alarmed - just alert to the mail: "If you don't feel comfortable opening it, don't."

But across the US, anxiety is strong.

Sometimes Cindy, a mother in the Washington DC area, says she does not get her letters out of the mailbox for an entire week. When she does, it is with plastic gloves, and carries the mail directly to the garage. There, she opens it away from her family and immediately throws out the envelopes before washing her hands and changing her clothes.

On one occasion she microwaved her mail, following reports it could kill anthrax, but then thought she might be contaminating an oven in which she cooks the family food. She has yet to convince her husband to buy a separate microwave for the mail.

"The more you hear about these reports that they can't find the source of the anthrax mail, the less I want to open my mail," says Cindy, who does not want to reveal her family name - for fear of a contaminated letter.

Other Americans say they have bought plastic gloves and masks as a precaution. Yet Wal-Mart, a barometer of nationwide retail trends, does not see a dramatic increase in the sales of either.

While many talk of taking extra steps to guard against cross-contamination, anecdotal evidence suggests few are taking action. Mohson Sufi of Houston says when he started to think twice about the mail he told himself, "this is ridiculous," and stopped watching the news.

Even many handling big volumes for companies are not bothering to protect themselves.

Dynegy, the US energy trader, says it offered gloves to those handling the 90,000 pieces of inbound monthly mail both before and after the September 11 terrorist attacks that set the stage for the anthrax scare. There were no takers.

"The last thing we want to do is overreact," says Milton Scott, Dynegy's chief administrative officer. "We have got a business to run."

Many seek comfort in seeing those most at risk - mail carriers - walking door to door, delivering mail in different parts of the country without so much as a pair of gloves.

A carrier in Arizona says she does not wear them because the nearest sorting hubs have declared their machinery free of anthrax.

In Houston, carriers report similar trust in the USPS to warn them if they need to be more careful.

Those in New York and Washington DC, where the targets of the anthrax mailings have been based, are more wary. But the USPS has not seen any trends toward more absenteeism or retirement by workers.

Nevertheless, the scare has made Lia, who works on Capitol Hill, hesitate to enter her building's post office.

"I thought about it a couple of times before mailing a letter," she says. "I decided to conquer my fear: I mailed it and felt proud."

That is what the USPS wants to see. "We're encouraging people to mail more cards this year than ever, to fly in the face of terrorism," says Mr Saunders. "Not mailing anything falls into their hands."

The national Greeting Card Association says 86 per cent of Americans are not concerned about handling or opening personal mail and less than 10 per cent will be sending fewer cards due to the anthrax scare.

Even Cindy is going to inflict cards on her friends and family, and is looking forward to receiving some herself. "A few Christmas cards is not going to make it any worse.," she says. "If you have to open the mail, you might as well get something pleasant in it."