The Italian businessman was sentenced to four-and-a-half years behind bars in December 2008 after pleading guilty to 14 counts of wire fraud, conspiracy and money laundering.
The Devil Wears Prada actress dumped Follieri in June 2008, shortly before he was arrested by federal authorities and admitted to scamming more than $3.6 million (£2.25 million) from investment and real estate firms.
The star has since embarked on a relationship with actor Adam Shulman - but Follieri has been finding it hard to move on, and regularly writes to Hathaway begging for a second chance, according to Britain's Sunday Express.
A source tells the publication, "Anne fears anything she says to him will lead to a fresh avalanche of mail. The letters are not only torturing Anne, they are putting pressure on her new relationship."