source: https://www.securityfocus.com/bid/1421/info

If an E-mail containing an excessively long To: field in the header (~1.5 MB) is processed by First Class Intranet Services (FCIS), a Denial of Service can occur.

https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/20052.tar.gz