tcp-env: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/tcp-env - from package: qmail
/var/lib/qmail/bin/tcp-env - from package: qmail

You may install the required package with command apt-get install {package}

Error in other languages:
tcp-env: bevel nie gevind nie
tcp-env: comandă negăsită
tcp-env: comando não encontrado
tcp-env: commande introuvable
tcp-env: command not found
tcp-env: käsku ei ole
tcp-env: không tìm thấy lệnh
tcp-env: komanda nerasta
tcp-env: Kommando nicht gefunden.
tcp-env: kommandot finns inte
tcp-env: komut yok
tcp-env: nie znaleziono polecenia
tcp-env: níor aimsíodh an t-ordú
tcp-env: no se encontró la orden
tcp-env: no s'ha trobat l'ordre
tcp-env: opdracht niet gevonden
tcp-env: parancs nem található
tcp-env: perintah tidak ditemukan
tcp-env: príkaz nenájdený
tcp-env: příkaz nenalezen
tcp-env: команда не найдена
tcp-env: командата не е открита
tcp-env: 命令找不到
tcp-env: コマンドが見つかりません