How to use dovecot only as POP3 server / prevent it from creating .imap directories?

[Binarus]

Dear all,

on our mail server, I let sendmail deliver incoming messages to a file in mbox format called "inbox" in each user's home directory.  Now I would like to use dovecot as POP3 server so that users can let their MUA download their messages via POP3. I do not want to use any IMAP functionality.

The POP3 part works with the configuration shown below, but nevertheless there is a problem which is a show stopper:

Although I think I have turned off IMAP (e.g. no IMAP listener), dovecot still creates .imap directories and does so in a very weird way. It creates one .imap subdirectory in every subdirectory of each user's home directory, and for every file in each user's home directory creates an additional subdirectory with the same name in its .imap directories. It does this recursively, and 1000 files in a user's home directory would mean 1000 additional subdirectories.

Of course, I can't live with that. I know that the dovecot documentation discourages using the home directory as mail location, but in my case this should not be a problem at all if IMAP is not used. I have played around with dovecot for several days, but could not solve that problem.

So how can I turn off IMAP completely and prevent dovecot from creating any .imap directories or IMAP related files?

This happens with dovecot 2.3.4.1 (f79e8e7e4) on Debian buster (with all updates applied).

My configuration (doveconf -n) is (the configuration is complete - I don't use SQL or LDAP):

# 2.3.4.1 (f79e8e7e4): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.4 ()
# OS: Linux 4.19.0-9-amd64 x86_64 Debian 10.4
# Hostname: host.example.com
listen = aaa.bbb.ccc.ddd
mail_location = mbox:~:INBOX=~/inbox
mail_privileged_group = mail
namespace inbox {
  inbox = yes
  location =
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix =
}
passdb {
  driver = pam
}
pop3_lock_session = yes
protocols = " pop3"
service imap-login {
  inet_listener imap {
    port = 0
  }
  inet_listener imaps {
    port = 0
  }
}
service pop3-login {
  inet_listener pop3 {
    port = 0
  }
  inet_listener pop3s {
    port = 995
    ssl = yes
  }
}
ssl = required
ssl_cert = </etc/dovecot/tls/xxxx.crt
ssl_cipher_list = DHE-RSA-AES256-GCM-SHA384
ssl_client_ca_dir = /etc/ssl/certs
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
ssl_min_protocol = TLSv1.2
ssl_prefer_server_ciphers = yes
userdb {
  driver = passwd
}

Thank you very much in advance for any idea!

Regards,

Binarus