[Mailman-Users] Mailman cannot deliver email to a particular domain

[Hung Phan]

We have a particular issue with Mailman (more of an exim issue actually) cannot delivers email to our canby.k12.... domain. Emails send to this domain come back with this error (-53): retry time not reached for any host. Other emails went out OK.

When we run the exim -d -M message_ID, here is a portion of the log file:

>>>>>>>>>>>>>>>> Remote deliveries >>>>>>>>>>>>>>>>
--------> csdadmin at canby.k12.or.us <--------
search_tidyup called
changed uid/gid: remote delivery to csdadmin at canby.k12.or.us with transport=remote_smtp
  uid=93 gid=93 pid=15280
  auxiliary group list: <none>
set_process_info: 15280 delivering 1VitQf-0003yJ-96 using remote_smtp
remote_smtp transport entered
  csdadmin at canby.k12.or.us
checking status of canby.k12.or.us
locking /var/spool/exim/db/retry.lockfile
locked /var/spool/exim/db/retry.lockfile
EXIM_DBOPEN(/var/spool/exim/db/retry)
returned from EXIM_DBOPEN
opened hints database /var/spool/exim/db/retry: flags=O_RDONLY
dbfn_read: key=T:canby.k12.or.us:10.30.XXX.XX
dbfn_read: key=T:canby.k12.or.us:10.30.XXX.XX:1VitQf-0003yJ-96
no message retry record
canby.k12.or.us [10.30.192.16] status = usable
10.30.XXX.XX in serialize_hosts? no (option unset)
delivering 1VitQf-0003yJ-96 to canby.k12.or.us [10.30.XXX.XX] (csdadmin at canby.k12.or.us)
set_process_info: 15280 delivering 1VitQf-0003yJ-96 to canby.k12.or.us [10.30.XXX.XX] (csdadmin at canby.k12.or.us)
set_process_info: 15279 delivering 1VitQf-0003yJ-96: waiting for a remote delivery subprocess to finish

The 10.30.xxx.xx is a masked IP to protect our DNS service. 

Our domain is canby.k12... while our email is canby.k12... and hosted by an external provider. According to the log file, it seems that Mailman thinks canby.k12... domain is hosted at 10.30.xxx.xx, which is our internal DNS service. Is there a tool for us to trace the email sending route? We suspect it is the DNS setting but need more info to determine where does it stop. Do we need an MX record, A record or something else in our DNS service so Mailman not try to connect to this DNS server and end up failing?

We can post the exim config file if needed.

Thank you very much for advice,