I guess (not sure) that you may have those libraries installed with different numerical suffixes. If that is the case make a symbolic link.
ln -s <source> <destination
for each file in /usr/lib/ or /usr/lib64/ directory depending upon your OS. Maybe it helps.
Else use remi and epel repos.
wget http://rpms.famillecollet.com/enterprise/remi-release-5.rpm wget http://download.fedora.redhat.com/pub/epel/5/x86_64/epel-release-5-3.noarch.rpm
rpm -Uvh remi*.rpm epel*.rpm
yum --enablerepo=remi install dovecot