[exim] Callouts that don't immediately work

Hi folks,

After recently configuring a new mail server (exim4-daemon-heavy
4.72-6 on Debian squeeze) with which I was quit satisfied, I was
informed that the system mail name (the domain name used to qualify
mail addresses without a domain name) had to be changed. After adding
the new domain name I ran some tests and noticed that the callouts
from other servers receiving from this one were not succeeding. No
idea why. The callout still worked for the old domain name. Using
telnet, I could run the callout procedure manually for addresses using
the new domain name, but that worked just fine.

Frustrated, I backed off and thought about it for a while. Then I ran
some more tests a few hours later... which all completed without any
problems. As if nothing had ever been the matter.

Is this normal behavior? Any explanations?

Thanks,

Jaap