mailq.postfix: 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/mailq.postfix - from package: postfix

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

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