Thx for your answer.
I've changed 'protocol managesieve {}' for 'protocol sieve {}', and now I get this error in my queue:

"1742368021D     3846 Sun Feb  5 20:25:10  MAILER-DAEMON
                                                           (temporary failure)
                                         www-data@smtp.domain.com"

Is there any tool to analyze the mail logs easily?, through the web interface, for example.

I've compared my dovecot.conf with your reference file, and I only see these lines added at the end of file:

protocol sieve {
  # Specify an alternative address:port the daemon must listen on
  # (default: *:2000)
  # listen = localhost:2000
  managesieve_logout_format = bytes ( in=%i : out=%o )
}

My dovecot.log file only shows lines like these:

Feb 07 17:37:53 pop3-login: Info: Login: user=<user@domain.com>, method=PLAIN, rip=xx.xx.xx.xx, lip=xx.xx.xx.xx, mpid=11455
Feb 07 17:37:53 pop3(user@domain.com): Info: Disconnected: Logged out top=0/0, retr=0/0, del=0/32, size=11900214

I also see this error continuously in my sieve.log file:

Feb 07 17:28:44 lda(www-data): Fatal: setgid(5000(vmail) from mail_gid setting) failed with euid=33(www-data), gid=4(adm), egid=4(adm): Operation not permitted (This binary should probably be called with process group set to 5000(vmail) instead of 4(adm))

Any solution?