nmap shows port 21 to be open

I ran the command

nmap localhost

on my Linux Ubuntu machine and got the following output

Other addresses for localhost (not scanned): ::1
rDNS record for 127.0.0.1: localhost.localdomain
Not shown: 983 closed ports
PORT     STATE SERVICE
21/tcp   open  ftp
22/tcp   open  ssh
25/tcp   open  smtp
53/tcp   open  domain
106/tcp  open  pop3pw
110/tcp  open  pop3
143/tcp  open  imap
465/tcp  open  smtps
587/tcp  open  submission
783/tcp  open  spamassassin
993/tcp  open  imaps
995/tcp  open  pop3s
3000/tcp open  ppp
3306/tcp open  mysql
8443/tcp open  https-alt
9080/tcp open  glrpc
9081/tcp open  unknown
 

I see that port 21 used by ftp and port 783 used by spamassain is open. FTP is unsecure and I wonder why the port is showing to be open. Normally I banned ftp per Plesk and only allowed there fdps. Spamassain grants itselve bin/bash rights. Thats why i see this also with an critical eye. How can I close these open ports?

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