The quota message should only appear in an Exchange Server enviroment. If the computer is configured to use an Exchange Server email system, your company's network person may be able to help you quickly resolve this.
Have a look into your inbox(es) and if multiple attachments seem to add up to many megabytes (1-200+), you can save the attachments yourself, then delete the original emails and keep the company network guy busy poking around another's PC besides yours.
The Dell network assistant can be removed from add/remove programs in control panel. Be sure to check Show Updates box in upper right to show all.
Good Luck!