I have exim4 (exim4-daemon-heavy) running on etch. This machine has only a few users who send directly. One of them has an ISP who seems to have a broken DNS setup. The symptom I see is that when this user connects to the server (port 25 or 587) there is a large delay before the 220 banner is shown e.g.: [snip] Is it possible to whitelist a range or turn off the check?
There is a debconf option that minimizes DNS lookups. It should solve this problem, but it might disable the lookups also in places where you might want them.
In any case, you can change the value of that option with dpkg-reconfigure exim4-config or by editing /etc/exim4/update-exim4.conf.conf .
-- Eduardo M KALINOWSKI eduardo@kalinowski.com.br