The following errors are shown in
/var/log/messages file, does it affect mail service functionality?
www postfix/smtpd: SQL engine 'intentionally disabled' not supported
www postfix/smtpd: auxpropfunc error no mechanism available
No, the issue does not affect mail service functionality, sqlite plugin has been used in Plesk 10.x versions, but Plesk 11 uses its own SASL auxprop plugin. The issue may occur if after Plesk upgrade from 10.x version or lower.
Such errors can be safely ignored, or or fixed with the following steps:
For RedHat, CentOS, CloudLinux, SuSE:
# rpm -e cyrus-sasl-sqlite3
For Debian, Ubuntu:
# dpkg --purge libsasl2-modules-sqlite3
Restart Postfix service:
# /etc/init.d/postfix restart
NOTE: If the package should be installed back for some reason, it can be found in Plesk repository, for example for CentOS 6, x86_64 and Debian 6.0, x86_64: