roundup-mailgw: 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/roundup-mailgw - from package: roundup

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

On Debian possible default full paths are:

/usr/bin/roundup-mailgw - from package: roundup

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

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