/etc/exim4/conf.d/acl/30_exim4-config_check_mail is in exim4-config 4.76-3ubuntu3.4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | ### acl/30_exim4-config_check_mail
#################################
# This access control list is used for every MAIL command in an incoming
# SMTP message. The tests are run in order until the address is either
# accepted or denied.
#
acl_check_mail:
.ifdef CHECK_MAIL_HELO_ISSUED
deny
message = no HELO given before MAIL command
condition = ${if def:sender_helo_name {no}{yes}}
.endif
accept
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