Eu costumo fazer como descrito abaixo:
domainlist local_domains = my.domain.com
hostlist relay_from_hosts = 127.0.0.1 : 192.168.0.0/16 : 10.0.0.0/8
domainlist relay_to_domains = my.relay1.domain.com : my.relay2.domain.com
...
begin acl
...
acl_check_rcpt:
...
# Allow authenticated users
accept authenticated = *
# Deny if sender isn't exist
accept hosts = +relay_from_hosts : \
${if exists{/etc/exim/host_whitelist} \
{/etc/exim/host_whitelist}{} }
endpass
message = sender mailbox not found
verify = sender
# Check if recipient exists in local and relay domains
accept domains = +local_domains : +relay_to_domains
endpass
message = recipient mailbox not found
verify = recipient
# Deny all others (this is the last checking rule)
deny message = relay not permitted
acl_check_predata:
...
Eu não estou usando destinatários verificando nas seções de transportes e roteadores. E isso funciona perfeitamente.