An update of my Debian or Ubuntu will remove Zarafa, what's the reason for this?

A update from Debian GNU/Linux 4.0r3 "Etch" and Ubuntu 8.04 will remove Zarafa, by upgrading libvmime0

Calculating upgrade... Done
The following packages will be REMOVED:
zarafa zarafa-webaccess
The following NEW packages will be installed:
libgsasl7
The following packages will be upgraded:
libvmime0
1 upgraded, 1 newly installed, 2 to remove and 0 not upgraded.
Need to get 944kB of archives.
After unpacking 16.2MB disk space will be freed.
Do you want to continue [Y/n]?

Since the libvmime API of 0.7 and 0.8 is completely different, we indeed hold the upgrade from Debian Etch back.

However, this is not an issue, since no other package in Debian depends on 0.8. You can set the libvmime0 package on hold with the command

echo libvmime0 hold | dpkg --set-selections