In 10.7 server, we had a great filter for vacation messages built into webmail.
Users could configure this quite easily.
I can't find either webmail or vacation messages in Mountain Lion Server 10.8.
OK - part two - to get managesieve plugin configured in Roundcube
In this file:
your path to webmail/plugins/managesieve/config.inc.php.dist make the following changes
// managesieve server port
$rcmail_config['managesieve_port'] = 4190;
$rcmail_config['managesieve_host'] = 'server.domain.com';
// authentication method. Can be CRAM-MD5, DIGEST-MD5, PLAIN, LOGIN, EXTERNAL
// or none. Optional, defaults to best method supported by server.
$rcmail_config['managesieve_auth_type'] = LOGIN;
// default contents of filters script (eg. default spam filter)
$rcmail_config['managesieve_default'] = '/var/lib/dovecot/sieve/default.sieve';
// The name of the script which will be used when there's no user script
$rcmail_config['managesieve_script_name'] = '';
// Sieve RFC says that we should use UTF-8 endcoding for mailbox names,
// but some implementations does not covert UTF-8 to modified UTF-7.
// Defaults to UTF7-IMAP
$rcmail_config['managesieve_mbox_encoding'] = 'UTF-8';
// I need this because my dovecot (with listescape plugin) uses
// ':' delimiter, but creates folders with dot delimiter
$rcmail_config['managesieve_replace_delimiter'] = '';
// disabled sieve extensions (, copy, date, editheader, encoded-character,
// envelope, environment, ereject, fileinto, ihave, imap4flags, index,
// mailbox, mboxmetadata, regex, reject, relational, servermetadata,
// spamtest, spamtestplus, subaddress, vacation, variables, virustest, etc.
// Note: not all extensions are implemented
$rcmail_config['managesieve_disabled_extensions'] = array();
// Enables debugging of conversation with sieve server. Logs it into <log_dir>/sieve
$rcmail_config['managesieve_debug'] = true;
// Script name extension used for scripts including. Dovecot uses '.sieve',
// Cyrus uses '.siv'. Doesn't matter if you have managesieve_kolab_master disabled.
$rcmail_config['managesieve_filename_extension'] = '.sieve';
// List of reserved script names (without extension).
// Scripts listed here will be not presented to the user.
$rcmail_config['managesieve_filename_exceptions'] = array();
In yourpathto webmail/plugins/managesieve/managesieve.php
* Loads configuration, initializes plugin (including sieve connection)
If you dont change this line, it wont load the config file we changed above!
And thats it!
Remember that you can't test vacation rules by sending a message to yourself - it has to be a different address to be responded to I had to read deep into the doco to find out why I wasnt triggering my vacation response!!
Good luck from Down Under