Kmail的身份验证机制需要一组库的支持，分别是： 

cyrus-sasl.x86_64 : The Cyrus SASL librarycyrus-sasl-devel.i686 : Files needed for developing applications with Cyrus SASLcyrus-sasl-devel.x86_64 : Files needed for developing applications with Cyrus                        : SASLcyrus-sasl-gssapi.i686 : GSSAPI authentication support for Cyrus SASLcyrus-sasl-gssapi.x86_64 : GSSAPI authentication support for Cyrus SASLcyrus-sasl-ldap.i686 : LDAP auxprop support for Cyrus SASLcyrus-sasl-ldap.x86_64 : LDAP auxprop support for Cyrus SASLcyrus-sasl-lib.i686 : Shared libraries needed by applications which use Cyrus                    : SASLcyrus-sasl-lib.x86_64 : Shared libraries needed by applications which use Cyrus                      : SASLcyrus-sasl-md5.i686 : CRAM-MD5 and DIGEST-MD5 authentication support for Cyrus                    : SASLcyrus-sasl-md5.x86_64 : CRAM-MD5 and DIGEST-MD5 authentication support for Cyrus                      : SASLcyrus-sasl-ntlm.i686 : NTLM authentication support for Cyrus SASLcyrus-sasl-ntlm.x86_64 : NTLM authentication support for Cyrus SASLcyrus-sasl-plain.i686 : PLAIN and LOGIN authentication support for Cyrus SASLcyrus-sasl-plain.x86_64 : PLAIN and LOGIN authentication support for Cyrus SASLcyrus-sasl-sql.i686 : SQL auxprop support for Cyrus SASLcyrus-sasl-sql.x86_64 : SQL auxprop support for Cyrus SASLcyrus-sasl-sysvinit.x86_64 : The SysV initscript to manage the cyrus SASL authd.

需要根据自己的情况安装。如果不确定直接执行sudo yum install cyrus-sasl*即可。