From Kolab Wiki
There are differnt options to solve this problem:
The first option is to abandon entropy from your system. You can do this by using following command:
Warning: using this hot fix reduces the security of all cryptographic applications on your system!!
mv /dev/random /dev/random.backup ln -s /dev/urandom /dev/random
You should prefer the second solution which is to add hardware entropy generator to your system.
All recent Intel, AMD and Via processors have such a device. On newer kernels you need to load
hw_random, or amd-rng or intel-rng
You can read more about this solutions in following article.