If you are not able to send/receive emails from domain and getting the following error:
exim_mainlogs as “R=dkim_lookuphost defer (-1): host lookup did not complete”
Then in order to get this issue resolved check your ./etc/resolv.conf file. If the resolvers are missing then you can put the public DNS like :
nameserver 4.2.2.1
nameserver 4.2.2.2
it should now fix your email send/receive issue.