smime_keys: 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 CentOS possible default full paths are:

/usr/bin/smime_keys - from package: mutt

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/smime_keys - from package: mutt

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

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