Brian West, a retired restaurant owner in Thailand, thought six weeks was plenty of time to renew his New York driver’s license. All he had to do was mail an application form and his vision test results to the Department of Motor Vehicles office in Brooklyn.

When he tried to do that last Friday, the post office near his home in Chiang Mai declined to send his documents.

Thailand Post, the country’s postal service, has stopped sending mail to the United States while its transportation partners adjust to President Trump’s decision to end duty exemptions for low-value imports. Many postal services around the world have done the same as they await clarity on how Mr. Trump’s executive order, which went into effect at midnight on Friday, will play out.

While some carriers say the suspensions are temporary, they have created headaches and confusion for people who had never thought twice about dropping a letter or parcel destined for the United States at their post office.

“It feels helpless to think I can’t send mail to the U.S.,” Mr. West said, adding that not everyone can afford to use a more expensive courier service, such as UPS or FedEx. He said he would wait a few more days, but if the suspension wasn’t lifted by then, he would have to shell out about $50 for a courier.