pflogsumm: 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/sbin/pflogsumm - from package: postfix-perl-scripts

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

On Debian possible default full paths are:

/usr/sbin/pflogsumm - from package: pflogsumm

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

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