ResolutionParallels Plesk Panel 18.104.22.168 for Linux - Qmail STARTTLS vulnerability fix has been available since June 01, 2011 through the Autoinstaller and vzpkg update.
[-] Qmail-TLS STARTTLS protocol plaintext command injection vulnerability fixed. More details: http://telussecuritylabs.com/threats/show/FSC20110309-02
Additional informationParallels Plesk Panel 22.214.171.124 for Linux- Qmail STARTTLS vulnerability fix
Parallels Plesk Panel 9.x and 10.x - Qmail-TLS STARTTLS vulnerability fix