[imp] Can't send big messages

[Santiago Andres Florez V]

Hi, I'm using Horde 2.1 with IMP 3.1 stable running on Debian (Woody
3.0). I can't send messages bigger than 1.5Mb for some reason. I don't
receive any response from the webserver (I get timeout when using a
squid-proxy) after a couple of minutes. I already incremented the upload
size value in php.ini. I can send small messages without any problem.
I thought it were a PHP problem, but I tried uploading big files using
PHP and it works perfectly.

Here's my Horde test.php output: 

Horde Versions
      * Horde: 2.1
      * Passwd: 2.1
      * Turba: 1.1
      * IMP: 3.1 (run IMP tests)

PHP Version
      * View phpinfo() screen
      * PHP Version: 4.1.2
      * PHP Major Version: 4.1
      * PHP Minor Version: 2
      * PHP Version Classification: release
      * You are running a supported version of PHP.

PHP Module Capabilities
      * FTP Support: Yes
      * Gettext Support: Yes
      * IMAP Support: Yes
      * LDAP Support: No
      * MCAL Support: No
      * Mcrypt Support: No
      * MySQL Support: Yes
      * PostgreSQL Support: No
      * XML Support: Yes

Miscellaneous PHP Settings
      * short_open_tag enabled: Yes
      * magic_quotes_runtime set to Off: Yes
      * file_uploads enabled: Yes

PHP Sessions
      * Session counter: 2
      * To unregister the session: click here

PEAR
      * PEAR - Yes
      * Recent PEAR - Yes
      * Mail::RFC822 - Yes
      * Log - Yes
      * DB - Yes


Do you have any idea about what's happening with Horde IMP? Thank you
very much.

Cheers,

Santiago Florez