The email, which Sveriges Radio (SR) was previously told did not exist, was recently obtained by the broadcaster from the Sweden's Defence Research Agency (Totalförsvarets forskningsinstitut, FOI).
The mail contains information which shows that the Swedish government had been informed that the agency planned to use a shell company, SSTI, to manage dealings with Saudi Arabia related to the construction of a weapons factory.
Ever since SR first reported on the Saudi arms scandal back in March, the government has continually denied knowing of any links to SSTI, which according to SR was established to avoid the deal resulting in any direct ties between the agency and the government.
Defence Minister Karin Enström, who took over after Sten Tolgfors resigned from the job shortly after the scandal emerged, was unable to explain why the document can't be found in the government office's registry.
"I operate on the assumption that both my ministry and other ministries follow existing rules for how documents are registered," she told SR.
The revelations about the missing document don't sit well with Green Party defence policy spokesperson Peter Rådberg, who wants to know how much Prime Minister Fredrik Reinfeldt knew about the plans to use a shell company to help the Saudis build the arms plant.
"He's said himself that he didn't know about it. Now the question is going to come to him directly. He needs to lay his cards on the table," Rådberg told the TT news agency.
"That the government offices didn't register or removed this type of document is incredibly serious."