Mail dropped through door slots across the country on Tuesday as postal workers made a small dent in the millions of letters, bills and flyers that went undelivered during the rotating strikes and lockout at Canada Post.

Letter carriers were back on their routes again, two days after Parliament passed legislation ordering 48,000 postal employees to return to work.

Some carriers complained they were not allowed to work overtime to restore service faster. Canada Post, however, said it’s too early to know if overtime is needed.

The Crown corporation repeated its plea for patience as it tackles a big backlog of mail either piled up inside regional plants or waiting to get in.

"We’re still trying to get a grasp of how much," Canada Post spokesman Anick Losier told CBC News from Ottawa.

She couldn’t estimate how much mail awaits — 60 per cent of mail goes through centres in Montreal and Toronto — but said on a normal day this time of year, between 20 million and 30 million pieces are delivered to Canadian homes and businesses.

Postal workers were locked out June 14 after 12 days of rotating strikes by members of the Canadian Union of Postal Workers.

Plant workers returned to sorting jobs on Monday and Canada Post has been trying to reopen street boxes as quickly as possible. People can start mailing letters, but Losier said they should expect a small delay.

As for the backlog, Losier said the plan is to deliver the oldest mail first, even flyers that are advertising sales that have already happened. She didn’t want to estimate when the postal service will be caught up, but said it could be at least two or three weeks.

Weighing need for overtime

Over the next few days, the corporation will assess how much mail has piled up, including mail sitting in trucks from local collections and the United States. Management will then decide if certain operational changes are needed.

Some letter carriers were delivering twice their usual loads on Tuesday and some were unhappy they couldn’t work overtime to reach all of their customers.

"In some places, Canada Post is telling letter carriers to bring back mail, even if they aren’t finished their route," said  Denis Lemelin, national president of the Canadian Union of Postal Workers.

"Piles of backlogged mail are sitting in postal depots while Canada Post pushes its employees around," he said.

The union said that in Montreal, Windsor, Hamilton, Scarborough, Ont., and Kitchener, letter carriers reporting for duty were instructed to return all their undelivered mail to their originating office after eight hours of work.

"Canada Post has an obligation to provide postal service to all citizens under the Canada Post Corporation Act," said Lemelin. "Instead, management continues to hold the public’s mail hostage."

"We’re very frustrated by the attitude of Canada Post," said Stephen Gale, president of the Fraser Valley West local of CUPW in B.C. He said he had members who doubted they could finish their routes Tuesday within eight hours.

"Some people won’t get their mail," Gale said. "That’s very upsetting."

Losier said overtime hasn’t been ruled out but Canada Post wants to know how much mail it’s dealing with first.

"It would not be financially responsible to start putting in overtime without knowing what’s coming in [from waiting trucks] – especially after losing $200 million during the work stoppage."

The $200 million estimate includes $41 million worth of long-term contracts that were cancelled by major corporate mailers, Losier said. Unknown numbers of individuals may also have abandoned the service for good for online banking and other services, she said.

Questioning old flyers

Union members also complained the first day back about being forced to deliver expired flyers, but Losier said it wasn't possible to weed those out.

Despite some concerns among union members, their national office received reports of a good reception from the public when letter carriers were back on the street again. In Surrey, B.C., on Tuesday, young letter carrier Devin Piper reported being applauded as she delivered mail to a school.

Restoring public confidence will be the challenge after Canada Post service has reached a standard of reliable service, Losier said.