Same exact problems here (and I dont see a more recent thread).

It looks to me like this is a cached response as I dont even see a delivery attempt, just instafail at 'lookuphost' without a reason. I do not think this is a resolver problem, I can look stuff up no problem, and ping it (careful, host(1) ignores /etc/hosts, so could be something hidden in there, not in my case), but I do not get a proper error response

Code:
2019-05-23 12:43:50 cwd=/tmp 4 args: send-mail -i -- [email protected]
2019-05-23 12:43:50 1hTqoo-0007EE-LC <= [email protected] U=root P=local S=517 T="test" for [email protected]
2019-05-23 12:43:50 cwd=/var/spool/exim 3 args: /usr/sbin/exim -Mc 1hTqoo-0007EE-LC
2019-05-23 12:43:50 1hTqoo-0007EE-LC ** [email protected] R=lookuphost T=remote_smtp: all hosts for 'mydomain.com' have been failing for a long time (and retry time not reached)
2019-05-23 12:43:51 cwd=/var/spool/exim 7 args: /usr/sbin/exim -t -oem -oi -f <> -E1hTqoo-0007EE-LC
2019-05-23 12:43:51 1hTqop-0007EN-0G <= <> R=1hTqoo-0007EE-LC U=mailnull P=local S=1866 T="Mail delivery failed: returning message to sender" for [email protected]

I can telnet to the mx record for the mydomain.com above port 25 no problem.

How do I force it to try again to see what the actual failing reason is? Setting log_selector to +all doesnt help with any additional detail.

[EDIT] *SOLVED*

Never saw this mentioned in the few threads about this problem here.

Code:
ßæÏ:



	
ßæÏ:

	
cd /var/spool/exim/db
rm wait-dkim_remote_smtp* retry* wait-remote_smtp*
service exim restart


And then new and queued mail got sent out (because whatever other underlying problem I had solved earlier with another change, but somehow exim didnt get told about it despite having restarted it a few times to increase logging or other reasons).



https://forums.cpanel.net/threads/dkim_lookuphost-issue.606047/