Yes, I know how to do this trick:
This is from the e-smith developers mailing list:
"I just noticed that large file attachments cause webmail to error. I
tracked this down to the default setting in PHP (which powers e-smith
webmail and most other groupware mailers) is set at a 2MB filesize
limit. This is easy to fix. Simply edit /etc/php.ini and change the
default entry (shown below) to whatever suits your needs and restart
httpd.
upload_max_filesize = 2M
It might be good to note that quite a few ISP's do place the receive
limit at 5M so maybe five meg is a better default.
http://netsourced.com/e-smith/howto/howto-webmail-attachment-size.html"
Timothée