Trying to prevent large file attachments in Squirrelmail, on U8.10S, is this a PHP issue?

I am using PHP5 on Ubuntu 8.10 Server, it is being used by Apache and Squirrelmail. I have tried setting the upload_max_filesize in the /etc/php5/apache2/php.ini file, but it only seems to apply after I upload the file. My goal is to prevent remote Squirrelmail users from attaching large files to the emails they are drafting. They have slow connections, and uploading a large file would effectively hang them. Here is my question originally posted to the Ubuntu Forum (before I began understand it was possibly a PHP issue): Is it possible to prevent Squirrelmail users from uploading large files to a server running Squirrelmail? My testing seems to indicate that the attachment size limits enforced by Squirrelmail take place *after* the file has been uploaded - at which time Squirrelmail aborts the entire message. I will have some remote users, and I do not want them to be able to upload files that are over a limit (say 10MB). If a remote user tries to attach a 500MB attachment to their email, I don't want them to upload the entire 500MB file, only to then have SM abort the message. I want it to fail immediately, or after the 10MB limit has been reached. I though there was a way to do this in Apache or PHP, but have been unable to find it. I am running Ubuntu Server 8.10 with Apache, Postfix, Dovecot, and Squirrelmail. Any suggestions on how to get the file attaching process to abort before it uploads the entire 500MB file? thanks!