/etc/exim4/conf.d/ is in exim4-config 4.76-3ubuntu3.
This file is owned by root:root, with mode 0o755.
..
/etc/exim4/conf.d/acl/
/etc/exim4/conf.d/acl/00_exim4-config_header
/etc/exim4/conf.d/acl/20_exim4-config_local_deny_exceptions
/etc/exim4/conf.d/acl/30_exim4-config_check_mail
/etc/exim4/conf.d/acl/30_exim4-config_check_rcpt
/etc/exim4/conf.d/acl/40_exim4-config_check_data
/etc/exim4/conf.d/auth/
/etc/exim4/conf.d/auth/00_exim4-config_header
/etc/exim4/conf.d/auth/30_exim4-config_examples
/etc/exim4/conf.d/main/
/etc/exim4/conf.d/main/01_exim4-config_listmacrosdefs
/etc/exim4/conf.d/main/02_exim4-config_options
/etc/exim4/conf.d/main/03_exim4-config_tlsoptions
/etc/exim4/conf.d/main/90_exim4-config_log_selector
/etc/exim4/conf.d/retry/
/etc/exim4/conf.d/retry/00_exim4-config_header
/etc/exim4/conf.d/retry/30_exim4-config
/etc/exim4/conf.d/rewrite/
/etc/exim4/conf.d/rewrite/00_exim4-config_header
/etc/exim4/conf.d/rewrite/31_exim4-config_rewriting
/etc/exim4/conf.d/router/
/etc/exim4/conf.d/router/00_exim4-config_header
/etc/exim4/conf.d/router/100_exim4-config_domain_literal
/etc/exim4/conf.d/router/150_exim4-config_hubbed_hosts
/etc/exim4/conf.d/router/200_exim4-config_primary
/etc/exim4/conf.d/router/300_exim4-config_real_local
/etc/exim4/conf.d/router/400_exim4-config_system_aliases
/etc/exim4/conf.d/router/500_exim4-config_hubuser
/etc/exim4/conf.d/router/600_exim4-config_userforward
/etc/exim4/conf.d/router/700_exim4-config_procmail
/etc/exim4/conf.d/router/800_exim4-config_maildrop
/etc/exim4/conf.d/router/850_exim4-config_lowuid
/etc/exim4/conf.d/router/900_exim4-config_local_user
/etc/exim4/conf.d/router/mmm_mail4root
/etc/exim4/conf.d/transport/
/etc/exim4/conf.d/transport/00_exim4-config_header
/etc/exim4/conf.d/transport/10_exim4-config_transport-macros
/etc/exim4/conf.d/transport/30_exim4-config_address_file
/etc/exim4/conf.d/transport/30_exim4-config_address_pipe
/etc/exim4/conf.d/transport/30_exim4-config_address_reply
/etc/exim4/conf.d/transport/30_exim4-config_mail_spool
/etc/exim4/conf.d/transport/30_exim4-config_maildir_home
/etc/exim4/conf.d/transport/30_exim4-config_maildrop_pipe
/etc/exim4/conf.d/transport/30_exim4-config_procmail_pipe
/etc/exim4/conf.d/transport/30_exim4-config_remote_smtp
/etc/exim4/conf.d/transport/30_exim4-config_remote_smtp_smarthost
/etc/exim4/conf.d/transport/35_exim4-config_address_directory