[exim] mx and local host error

I have an Exim 4.69 test server running as a gateway (filter server)
which filters and passes messages onto our internal server. I have
been periodically getting a few messages frozen with the error:

     sample@???: lowest numbered MX record points to local host

The MX records for spis.net are set up as such:

spis.net.               3600    IN      MX      10 smtpgate.ndunet.com.
spis.net.               3600    IN      MX      10 smtpgate.yournetplus.com.
spis.net.               3600    IN      MX      20 smtpgate.ndunet.com.

smtpgate.yournetplus.com happens to be the server these errors are
occuring on.

I believe this has something to do with how the router section is set
up but can not pinpoint what. Here is the router section:

begin routers

relay_to_domains:
   driver     = manualroute
   transport  = remote_smtp
   route_data = ${lookup{$domain}lsearch{/usr/local/etc/exim/relay_to_domains}}
   ignore_target_hosts = +bad_host_addresses

dnslookup:
driver = dnslookup
domains = ! +local_domains
transport = remote_smtp
ignore_target_hosts = +bad_host_addresses
no_more

system_aliases:
driver = redirect
allow_fail
allow_defer
data = ${lookup{$local_part}lsearch{/etc/aliases}}
user = mailnull
group = mail
file_transport = address_file
pipe_transport = address_pipe

userforward:
driver = redirect
check_local_user
file = $home/.forward
no_verify
no_expn
check_ancestor
file_transport = address_file
pipe_transport = address_pipe
reply_transport = address_reply
condition = ${if exists{$home/.forward} {yes} {no} }

localuser:
driver = accept
check_local_user
transport = local_delivery
cannot_route_message = Unknown user

relay_to_domains contain entries like such:

spis.net: 162.42.148.120

bad_host_addresses contain a list of IP addresses in CIDR format of
the IANA private IP space (internal or reserved).