One user started receiving thousands of 'bounced' email messages per day. I changed the Webmail message display option from 50 to 999 so they could more quickly scan and delete the bogus messages. Then the Inbox and some other folders would timeout when selected and leave the toolbar area of the web page blank. I then changed the message display option from 999 to 500 and the problem seems to be fixed. This may, or may not, be a real fix.