[imp] Problem sending mails when big attachments should be automatically linked

[Jens Grüntjes]

Hello list,

I'm using IMP 6.1.0 and Horde Groupware Webmail Edition 5.1.0.

I have a problem whenever I try to attach a file bigger than  
$conf[compose][link_attach_threshold] which is 3,000,000 bytes in my  
case. In the compose window the attachment is attached to the mail, at  
least that is displayed in a green info-box. When I press "Send" a red  
alert box is popping up saying "Unable to open VFS file". The horde  
log says something similar:

2013-06-11T06:25:00+00:00 DEBUG: HORDE [imp] Unable to open VFS file.  
[pid 6437 on line 27 of  
"/usr/share/php/Horde/Core/Notification/Handler/Decorator/Hordelog.php"]

The VFS in Horde is configured like this:
$conf['vfs']['params']['vfsroot'] = '/tmp';
$conf['vfs']['type'] = 'File';

The file is uploaded in my temp-directory which is located at /tmp.  
More exactly the file is uploaded to the directory  
/tmp/.horde/imp/attachments/my_user. All the directories starting from  
/tmp/.horde are owned by the user that runs the web server (www-data).

I thought that if the file was uploaded then it should be readable to  
horde and the web server. I'm a little confused and I hope you can  
help me out.

--
Greetings
Jens