John Franks wrote:
> Backing out of the krb5-libs packages permitted dovecot to work again.
Answering my own question I found the following CentOS web page which
solved the problem.
http://wiki.centos.org/Manuals/ReleaseNotes/CentOS5.1/
In the "Known Issues" Section I found:
"The Dovecot package on x86_64 kernels requires the parameter
"login_process_size = 64" to be added to /etc/dovecot.conf after an
upgrade to CentOS 5.1."
which seems to have resolved the issue.