"host lookup did not complete" error

check if MX DNS resolution fails from your side or not with mxtoolbox.com

• if you don't have MX results. exim should fallback to A record. cf exim FAQ (check Q0311 too)

use exim -bt -d-resolver [email protected] to diagnose exim mail routing

• if yes. it means DNS resolution fails on your side.

run nslookup -type=MX example.org on your server. and check if you get MX records answers.

if not, try the same request but specify a well known nameserver, like google public dns: nslookup -type=MX example.org 8.8.8.8

you should now get some MX results, and it means your nameserver is not working properly. So you can change your resolv.conf to a nameserver that works properly (provider, google dns, what you want, ..) or setup your own