The German company's deal with Jordan expired at the end of last season. The news is a huge blow as Jordan have already admitted that they are finding it hard to raise the funds to compete next year. Their second driver berth has effectively turned into a race for sponsorship for those hoping to land it.
They are Japanese Takuma Sato, who may be dropped despite being under contract, and Britons F1 veteran Eddie Irvine and rookie Anthony Davidson.
Deutsche Post, who had been Jordan's main sponsor for three years, said the end of the current contract had seemed "a good time to stop" the association.
"We have totally achieved our goals in terms of communication," Deutsche Post spokesman Gert Schukies said in a statement.
"Participating in motor racing has enabled us to make our brand known internationally."
He added: "Jordan Ltd were fair and communicative partners throughout our three years of collaboration."
Jordan team boss Eddie Jordan said he had known for a while that the contract would not be renewed.
He said in a statement that he was already in negotiations with potential new sponsors.
"Although this past season was not among our most competitive, the fact that we finished in the top six for a ninth consecutive season shows that even in difficult times we have acquitted ourselves well," added Jordan.