Shares in Deutsche Post have fallen by as much as 5% after the company warned that its operating profits in the current year would be flat.
Deutsche Post has been expanding outside its key German market
The German postal giant said it expected to report earnings before interest and tax of 3.7bn euros ($4.4bn; £2.5bn) in 2006.
That compares with a similar figure of 3.76bn euros for the previous year.
Although Deutsche Post has forecast a strong rise in sales, its DHL logistics division has been struggling in the US.
Deutsche Post has been expanding its presence abroad in order to reduce its reliance on its core German market.
In September last year, it bought UK logistics group Exel for £3.8bn, creating the world's biggest logistics, sea and air freight group.