router/350_local_virtual_domains

virtual_domains:
  debug_print = "R: virtual domains for $local_part@$domain"
  driver = redirect
  allow_fail
  allow_defer
  domains = dsearch;CONFDIR/virtual
  qualify_preserve_domain
  data = ${lookup {$local_part} lsearch {CONFDIR/virtual/$domain}}
  #no_more

There is now on standard alias file for each domain in CONFDIR/virtual/$domain. With no_more disabled there is a fallback to /etc/aliases.

each virtual domain has a file named CONFDIR/virtual/<DOMAIN>/aliases. This allows for different configuration options like message size or spam handling options on a per-domain basis:

350_local-config-virtual-users

# 350_local-config-virtual-users
#################################

# This router takes care of all domains configured in
# /etc/exim4/virtual/DOMAIN/
# it expects an aliases file in this directory and returns a list
# of local users.

virtual_users:
  debug_print = "R: virtual_users for $local_part@$domain"
  driver = redirect
  allow_defer
  allow_fail
  # get the domains this router is responsible for
  domains = dsearch;CONFDIR/virtual
  # resolve aliases from this file
  data = ${expand:${lookup{$local_part}lsearch*@{CONFDIR/virtual/$domain/aliases}}}
  # do not try to "fully qualify" an email address -- just take it as it is
  qualify_preserve_domain
  retry_use_local_part
  # this router is authoritative for this domain - stop after here
  no_more