iRedMail uses Amavisd-new + SpamAssassin to detect spams, and it also:

• Add '**** SPAM ****' in mail subject by default

• Add 'X-Spam-Status' in mail HEAD.

If you want to move spam mails into Junk folder, here are steps:

• Make sure your domain name is listed in /etc/amavisd.conf (RHEL/CentOS) or /etc/amavis/conf.d/50-user (Debian/Ubuntu). e.g.

@local_domains_maps = ['demo.iredmail.org', 'a.cn'];

• Find location of global sieve rule file in /etc/dovecot.conf (RHEL/CentOS) or /etc/dovecot/dovecot.conf (Debian/Ubuntu): sieve_global_path, default is /var/vmail/sieve/dovecot.sieve.

protocol lda {
    # ... SKIP OTHER SETTINGS HERE ...
    sieve_global_path = /var/vmail/sieve/dovecot.sieve
}

• iRedMail copies a sample file in the same directory by default, filename is /var/vmail/sieve/dovecot.sieve.sample. Rename it to the correct filename. If you can't find the sample file, you can also download it here.

• Restart dovecot service, and it should work for you now. If it doesn't work for you, please try to debug dovecot and find the root case from log files.