It is alleged that a software company paid the Guptas "commissions" to help it score Transnet contracts.
The former finance minister says the email is clearly a fabrication and is "worrisome".
The public protector will probe claims stemming from the Gupta leaks reports.
More explosive new information about how the Guptas captured Eskom and were allegedly involved in R17.4 billion in overpayments to Transnet. Meanwhile, Winnie Madikizela-Mandela gets frank about Madiba.
Its dossier alleges that Malusi Gigaba, Jacob Zuma and Brian Molefe were among those involved in the process.
Leaked emails show how Malusi Gigaba and Lynne Brown allegedly allowed the Guptas to infiltrate state-owned enterprises.
We spoke to amaBhungane’s Craig McKune, who outlined what was in the Gupta’s emails and what they mean for State Capture.
Gigaba's appointment as public enterprises minister marked the start of a "systematic process of reconfiguring" the boards of SOEs to ensure compliance, the report alleges.
Attempting to connect the dots, researchers and academics from four SA universities explain the assault on the South African state.