Dovecot upstream has found and fixed an off by one flaw in the dovecot server when the mmap_disable=yes setting is used in the dovecot configuration file. More information can be found in the upstream announcement: http://www.dovecot.org/list/dovecot-news/2006-November/000023.html This flaw also affects FC5
dovecot-1.0-1.rc15.fc6 has been pushed for fc6, which should resolve this issue. If these problems are still present in this version, then please make note of it in this bug report.
dovecot-1.0-0.beta8.3.fc5 has been pushed for fc5, which should resolve this issue. If these problems are still present in this version, then please make note of it in this bug report.