rcvsearch: 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/share/doc/mh-book/examples/mh/bin/rcvsearch - from package: mh-book

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

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