This rather sounds like a mis-configured/broken vacation binary.

Please create a separate ticket for this.

I tried to select all types of db, all worked ok for me, only 
difference, with empty, the .vacation.db, .vacation.dir and 
.vacation.pag were null in size when uploaded to account (I guess 
thats ok) with other db types the files vary in size (4096, 8162 and 
12288k) I guess you should modify the conf.xml, seems like qmail 
driver use forward driver.
Yes. When selected, horde-vacation default sets the accrual users 
email address as from address when sending out of office bounce mail. 
If not selected, from address is domain.com@mail.domain.com. I dont 
know why, I guess horde-vacation (or my vacation binary) dont get any 
data so it use some default value.

I then hide "change from address" options for end user (vacation gets 
messy if they change address, mailserver does not allow sending emails 
without valid user)

- - -

When testing dbtypes I found one strange thing. If you enable a 
vacation message, then go back to vacation and change the message and 
choose "Set/install vacation notice" click submit, then the new 
updated message gets uploaded, great, however, horde-vacation seems to 
check if any .qmail file exists on server, if do, renames old to 
.qmail_horde. Then disable the vacation message, all files on server 
gets removed except the .qmail file. I have to manually remove it to 
get rid of it. If not, server continue to sending vacation messages. 
If i try to enable vacation message again, horde-vacation does the 
same and leave the .qmail file when disable vacation message.

So, could we as well hard-code the database type to "empty", instead 
of changing conf.xml? Does Qmail work with any other database type at 
all?

Sorry, I don't get this. First you configure vacation to *show* the 
subject and from fields, and then you *remove* those fields from the 
form manually?

Hi,

To get horde-vacation to work properly (upload all vacation files to 
account), I had to insert this xml code (found here below), put it 
last in the "FTP driver for qmail compliant mailers" block (copied 
from the "FTP driver for dot-forward compliant mailers" block)

After that, when saved configuration for vacation, this is added to conf.php:
$conf['server']['params']['default']['dbtype'] = 'empty';
and it works as expected.

Below is xml code:

       <configenum name="dbtype" desc="The type of database file to use">empty
        <values>
         <value desc="An empty file">empty</value>
         <value desc="Berkeley DB 2.x hash, little endian">hash</value>
         <value desc="Berkeley DB 3.x hash, little endian">hash3</value>
         <value desc="Berkeley DB 4.x hash, little endian">hash4</value>
         <value desc="Berkeley DB 4.x hash, big endian">hash4b</value>
         <value desc="Berkeley DB 2.x btree, little endian">btree</value>
         <value desc="GNU dbm (gdbm) database, little endian">gdbm</value>
         <value desc="GNU dbm (gdbm) database, big endian">gdbmb</value>
        </values>
       </configenum>

I had to modify horde/vacation/lib/Driver/qmail.php to get working 
directory path
for mailbox, (.maildir insted of Maildir) 2 places.
Maybe this is not a bug but should help others, be documented at horde wiki.

I allso had to have:
$conf['vacation']['subject'] = true;
$conf['vacation']['from'] = true;
otherwise the bounce mail to sender had wrong from address. (could be 
error in my vacation binary, or configuration on server, so not sure 
this is a horde-vacation bug) Maybe god info for horde vacation wiki?

At last, to get clean vacation form, I modified:
horde/vacation/templates/main

diff -ur main.inc.dist main.inc
--- main.inc.dist       2009-05-07 17:27:47.000000000 +0200
+++ main.inc    2010-05-10 13:40:06.000000000 +0200
@@ -54,17 +54,17 @@

  <?php if ($GLOBALS['conf']['vacation']['subject']): ?>
  <p>
-<?php echo Horde::label('subject', _("Subject:")) ?>
+
  <br />
-<input name="subject" id="subject" type="text" size="70" value="<?php 
echo htmlspecialchars($cursubject) ?>" />
+<input name="subject" id="subject" type="hidden" size="70" 
value="<?php echo htmlspecialchars($cursubject) ?>" />
  </p>
  <?php endif; ?>

  <?php if ($GLOBALS['conf']['vacation']['from'] && 
$driver->hasCapability('changeFrom')): ?>
  <p>
-<?php echo Horde::label('from', _("From:")) ?>
+
  <br />
-<input name="from" id="from" type="text" size="70" value="<?php echo 
htmlspecialchars($curfrom) ?>" />
+<input name="from" id="from" type="hidden" size="70" value="<?php 
echo htmlspecialchars($curfrom) ?>" />
  </p>
  <?php endif; ?>

This is maybe not a bug but could help others, if added to 
horde-vacation wiki.

If you have any questions, just ask.