According to the RH website
(https://bugzilla.redhat.com/bugzilla/sh ... i?id=91933) the RPM
and associated SRPM will generate errors when it is running on a
vanilla kernel or a processor other than Intel. The suggestions are to
compile Berkeley DB with a different set of options or to get the RPM
from another site http://tomi.nomi.cz/download/db4-no-nptl/ .

After some googling it seams to me that this is the problem causing my
cyrus-imapd not to work.

If you are using a 2.6 kernel or Fedora, you need to do "mv /lib/tls /lib/tls-disabled" as noted in the 2.6 kernel announcements since UML doesn't support TLS.