dovecot: 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/dovecot - from package: dovecot

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

On Debian possible default full paths are:

/usr/sbin/dovecot - from package: dovecot-core
/usr/lib/debug/usr/sbin/dovecot - from package: dovecot-dbg

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

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