You installed iRdMail on this server twice, it's safe to remove duplicate settings.

I've removed one entry. Now my entry look like these:

protocol managesieve {
    # IP or host address where to listen in for connections.
    listen = 127.0.0.1:2000

    # Specifies the location of the symbolic link pointing to the
    # active script in the sieve storage directory.
    #sieve = dovecot.sieve
    #sieve = /var/vmail/sieve/%Ld/%Ln/dovecot.sieve
    sieve = /home/vmail/sieve/%Ld/%Ln/dovecot.sieve

    # This specifies the path to the directory where the uploaded scripts are stored.
    sieve_storage = /home/vmail/sieve/%Ld/%Ln/

    # Login executable location.
    login_executable = /usr/lib/dovecot/managesieve-login

    # managesieve executable location. See mail_executable for IMAP for
    # examples how this could be changed.
    mail_executable = /usr/lib/dovecot/managesieve

    # Maximum managesieve command line length in bytes.
    managesieve_max_line_length = 65536

    # To fool ManageSieve clients that are focused on CMU's timesieved
    # you can specify the IMPLEMENTATION capability that the dovecot
    # reports to clients (e.g. 'Cyrus timsieved v2.2.13').
    managesieve_implementation_string = dovecot
}

Now I've three further questions:

1. Where I've to put the personal dovecot.sieve script? When I put these in sieve = /home/vmail/sieve/DOMAIN/USERNAME/dovecot.sieve it dosen't work. But it seems to work here /home/vmail/sieve/dovecot.sieve

2. The following entry seems not to work:
if address :is "from" "income@email.de" {
  redirect "new@email.de;
}

But it should work according do the documentation...?!?

3. When I want to manage the sieve files with roundcube, I find a roundcube.sieve script in /home/vmail/sieve/DOMAIN/USERNAME/ does the iRedmail configuration read this script also or do I have to change something?
I also recognized, that when I save a sieve script in roundcube, a message said, "Unable to save filter. Server error occurred" but I found the script in /home/vmail/sieve/DOMAIN/USERNAME/
Any suggestions?

Thanks for your help!

i try to manage personal sieve files. but i don't know where to put theses files? just like in a "normal" installation in the user directory as .sieve-mail-filter?

And I also looked up the /etc/dovecote file.
There I have found 2 entries for managesieve:

# Provided services.
protocols = imaps managesieve managesieve

[...]

protocol managesieve {
    # IP or host address where to listen in for connections.
    listen = 127.0.0.1:2000

    # Specifies the location of the symbolic link pointing to the
    # active script in the sieve storage directory.
    #sieve = dovecot.sieve
    sieve = /var/vmail/sieve/%Ld/%Ln/dovecot.sieve

    # This specifies the path to the directory where the uploaded scripts are stored.
    sieve_storage = /home/vmail/sieve/%Ld/%Ln/

    # Login executable location.
    login_executable = /usr/lib/dovecot/managesieve-login

    # managesieve executable location. See mail_executable for IMAP for
    # examples how this could be changed.
    mail_executable = /usr/lib/dovecot/managesieve

    # Maximum managesieve command line length in bytes.
    managesieve_max_line_length = 65536

    # To fool ManageSieve clients that are focused on CMU's timesieved
    # you can specify the IMPLEMENTATION capability that the dovecot
    # reports to clients (e.g. 'Cyrus timsieved v2.2.13').
    managesieve_implementation_string = dovecot
}
protocol managesieve {
    # IP or host address where to listen in for connections.
    listen = 127.0.0.1:2000

    # Specifies the location of the symbolic link pointing to the
    # active script in the sieve storage directory.
    sieve = dovecot.sieve

    # This specifies the path to the directory where the uploaded scripts are stored.
    sieve_storage = /home/vmail/sieve/%Ld/%Ln/

    # Login executable location.
    login_executable = /usr/lib/dovecot/managesieve-login

    # managesieve executable location. See mail_executable for IMAP for
    # examples how this could be changed.
    mail_executable = /usr/lib/dovecot/managesieve

    # Maximum managesieve command line length in bytes.
    managesieve_max_line_length = 65536

    # To fool ManageSieve clients that are focused on CMU's timesieved
    # you can specify the IMPLEMENTATION capability that the dovecot
    # reports to clients (e.g. 'Cyrus timsieved v2.2.13').
    managesieve_implementation_string = dovecot
}

I also recognized, that the folder /var/vmail/sieve/ do not exist. But i have such a folder in /home...
so /home/vmail/sieve...

Normal email delivery work. There are also entries in the /var/log/sieve.log which look like:

deliver(email@address): Jan 10 20:38:21 Info: msgid=<462736772.33n26@blabla.de>: saved mail to INBOX