newaliases: command not found

Have You tried accessing the binary with the full path?

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

[root@server ~]# echo $PATH

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/newaliases - from package: exim
/usr/bin/newaliases - from package: opensmtpd
/usr/bin/newaliases - from package: ssmtp

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

On Debian possible default full paths are:

/usr/bin/newaliases - from package: dma
/usr/bin/newaliases - from package: esmtp-run
/usr/bin/newaliases - from package: exim4-daemon-heavy
/usr/bin/newaliases - from package: exim4-daemon-light
/usr/bin/newaliases - from package: masqmail
/usr/bin/newaliases - from package: msmtp-mta
/usr/bin/newaliases - from package: nullmailer
/usr/bin/newaliases - from package: postfix
/usr/sbin/newaliases - from package: courier-mta
/usr/sbin/newaliases - from package: qmail-run
/usr/sbin/newaliases - from package: sendmail-bin
/usr/sbin/newaliases - from package: ssmtp
/var/lib/qmail/bin/newaliases - from package: fastforward

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