[imp] Problem with atachment

[Martins Purins]

Hello.
We allow our clients mails up to 20Mb each. Now, I tested IMP with a 
17MB attachment and got errors

PHP Version: 4.3.2
     * Horde: 2.2.7
     * IMP: 3.2.7 (run IMP tests)
     * Turba: 1.2.1
     * Passwd: 2.2.1

LimitRequestBody 25242880
post_max_size = 25M
upload_max_filesize = 25M

Atached File size ~17MB

memory_limit = 8M
I have get error like this
Fatal error: Allowed memory size of 8388608 bytes exhausted (tried to 
allocate 17269036 bytes) in /var/www/html/horde/imp/compose.php on line 331

Then I set
memory_limit =32M
Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to 
allocate 23025385 bytes) in /var/www/html/horde/imp/compose.php on line 357

And finally I set
Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to 
allocate 46658595 bytes) in /var/www/html/horde/imp/compose.php on line 906

All three times I try send the same file, but without result. Any 
suggestions?