Start an interactive debugging fake-session for lookups only (hence the -all):
exim -d-all+lookup -bhc IP_ADDRESS
Selectors are as follows:
acl | ACL interpretation |
auth | Authenication |
deliver | General delivery logic |
dns | DNS lookups |
dnsbl | DNS black list code |
exec | Arguments for exec() |
expand | Details of string expansion |
filter | Filter handling |
hints_lookup | Hints data lookup |
host_lookup | All types of name-to-IP address handling |
ident | ident lookups |
interface | Lists of local interfaces |
lists | Matching things in lists |
load | System load checks |
local_scan | Debugging in the local_scan() function |
lookup | General lookup code and all lookups |
memory | Memory handling |
pid | Add pid to debug lines |
process_info | Setting info for the process log |
queue_run | Queue runs |
receive | General message reception logic |
resolver | The DNS resolver’s debugging output |
retry | Retry handling |
rewrite | Address rewriting |
route | Address routing |
timestamp | Timestamp debug lines |
tls | TLS logic |
transport | Transports |
uid | Change of uid/gid and looking up uid/gid |
verify | Address verification |
all | All of the above and also -v output |
Taken from here