[Mailman-Users] Emails to a specific email domain get error

[Hung Phan]

Hello,

We are having an issue with messages sent out through Mailman server that don't reach a specific email domain. In the exim main log, we see these error messages repeatedly show up:

email at thatdomain.com R=dnslookup T=remote_smtp defer (-53): retry time not reached for any host
or
email at thatdomain.com R=dnslookup T=remote_smtp defer (110): Connection timed out

Our Mailman server is not on any blacklist. What would likely be the issue here?


Thank you in advance for any advice,