mdo
A user rang to report a slow Internet connection and our investigation showed that they had accidentally sent out an email with 7MB attachment to a mailing list of about 300 recipients. The server was fighting against the limit in the broadband connection's upload speed.
While it is appropriate to delete emails and to teach users not to send large attachments to mailing lists, it does not solve the issue of bandwidth utilisation.
See
http://wiki.contribs.org/Wondershaperand there is also a newer contrib rpm in smecontribs repo (smeserver-htbwshaper-1.0-7.el4.sme.noarch.rpm ), so just do
yum install --enablerepo=smecontribs smserver-htpshaper
Configure appropriately for your upload bandwidth and in future even if a user does something inappropriate, your system will still function adequately.
You can also configure the number of concurrent email messages being sent by the system, to reduce the email load on your system at any point in time, search here for details.