--- /dev/null
+
+### router/850_exim4-config_lowuid
+#################################
+
+.ifndef FIRST_USER_ACCOUNT_UID
+FIRST_USER_ACCOUNT_UID = 0
+.endif
+
+.ifndef DEFAULT_SYSTEM_ACCOUNT_ALIAS
+DEFAULT_SYSTEM_ACCOUNT_ALIAS = :fail: no mail to system accounts
+.endif
+
+COND_SYSTEM_USER_AND_REMOTE_SUBMITTER = "\
+ ${if and{{! match_ip{$sender_host_address}{:@[]}}\
+ {<{$local_user_uid}{FIRST_USER_ACCOUNT_UID}}}\
+ {1}{0}\
+ }"
+
+lowuid_aliases:
+ debug_print = "R: lowuid_aliases for $local_part@$domain (UID $local_user_uid)"
+ check_local_user
+ driver = redirect
+ allow_fail
+ domains = +local_domains
+ condition = COND_SYSTEM_USER_AND_REMOTE_SUBMITTER
+ data = ${if exists{/etc/exim4/lowuid-aliases}\
+ {${lookup{$local_part}lsearch{/etc/exim4/lowuid-aliases}\
+ {$value}{DEFAULT_SYSTEM_ACCOUNT_ALIAS}}}{DEFAULT_SYSTEM_ACCOUNT_ALIAS}}