[imp] Cannot download large folder

[Otto Stolz]

Hello,

still using
- Horde 3.1.3,
- Imp H3 (4.1.3),
- Apache 2.2,
- PHP 5.2.0,
- PEAR 1.4.11 (with Mail 1.1.14, HTTP_Request 1.4.0, Net_IMAP 1.0.3,
   File 1.2.2, and File_Find 1.3.0),
- and Linux (2.6.18.8 kernel), distributed as openSUSE 10.2 (i586).

One of my customers cannot download a large folder
(“du” command reports: “81M”), whilst he has successfully
downloaded two smaller folders. The user reports that
he sees, whenever he has hit the “Download Folder(s)” button,
after the “All messages ... will be downloaded” popup,
a blank page.

Grepping various configuration files for the catchwords
“limit”, “size”, and “stor”, I have found:
- in horde/config/conf.php:
   $conf['session']['cache_limiter'] = 'nocache';
- in horde/imp/config/conf.php:
   $conf['fetchmail']['size_limit'] = '4000000';
   $conf['compose']['attach_size_limit'] = '51904512';
- in /etc/php5/apache2/php.ini
   memory_limit = 128M
   post_max_size = 8M
   upload_max_filesize = 50M
   session.cache_limiter = nocache
- nothing in /etc/apache2/*.conf

Now the question is, where is a size limit I should mend?
Could it even be a limit of the remote IMAP server?

Thanks for any hint,
   OttO Stolz