The post office could be going the way of the pony express.

A day after Postmaster General John Potter threatened to cut mail delivery from six to five days a week, postal experts, direct marketing executives and politicians alike said the outlook for the quasi-governmental U.S. Postal Service is bleak.

"It certainly represents a divergence of mail service as we know it," Postal Regulatory Commission Chairman Dan Blair told FOXNews.com of the potential move to five-day service as a cost-cutting measure. "But we don't really rely on mail the same way we do today as we did five, 10 years ago. Our expectations of postal service are different from a generation ago."

Illinois Rep. Danny Davis, chairman of the Federal Workforce, Postal Service and the District of Columbia subcommittee, said it's a matter of unavoidable truths.

"We've seen this coming for several years now, quite frankly," Davis told FOXNews.com. "The volume simply is not there; e-commerce has taken its toll. We used to write letters to grandma and stuff like that, now we just don't do that anymore. You can't deliver what's not there."

Citing inflating costs, a $6 billion budget deficit and the largest annual decrease in mail volume ever, Blair said the Postal Service has entered uncharted territory, even worse than in the 1990s, when the USPS considered eliminating window services.

Click here for a video of Blair.

"This is different because we've seen a decline in volume across all classes in percentages not seen since the Great Depression," Blair said. "You couple that with the decline in first-class mail as well … the mail mix isn't as profitable for them as it once was."

Cutting a day of service would have to be approved by Congress and postal officials, but it could save roughly $1.9 billion a year, Blair said.

Still, with postal rates expected to rise in mid-May, it'll be a hard sell to the American public.

"If it was a normal business, their customers would turn to someone else," Blair said.

During testimony before a Senate subcommittee on Wednesday, Blair said eliminating a day of mail service may expedite the decline of mail volume and suggested that the closure of some post offices should be considered.

"That's something I would recommend," Blair told FOXNews.com. "[But] this raises serious public policy implications. In rural America, the post office is the face of the American government. Closing post offices brings out very parochial concerns. It's an area where they could save money, but it's an area that will receive a lot of political attention."

Bob Cohen, a former Postal Regulatory Commission official, was even more pessimistic about the agency's future.

"The model may be in jeopardy now," Cohen told FOXNews.com. "They've got a problem. As the role of the postal service becomes less and less important as a communications medium, I guess it's going to have to shrink. It's very foggy right now what the future is."

But Jerry Cerasale, senior vice president of government affairs at Direct Marketing Association, said eliminating a mail day — possibly Tuesday, the slowest mail day of the week, or Saturday — could seriously affect direct-mail firms, periodicals and other firms that utilize mail.

"This is not the time for the postal service to raise rates and cut service," Cerasale told FOXNews.com. "It puts us in a very difficult place."

Perhaps more troubling than the specter of losing a day to reach customers is an estimated volume drop of 14 billion pieces of mail for fiscal year 2009, Cerasale said.

"That for us is big news," he said. "Many firms who use mail don't come back because they find other ways to reach their potential customers."