Please make sure that you have all the following:
(1) Server's full name, mhost.math.ias.edu, in your Netscape for both incoming and outgoing email servers.
Click Edit -> Preferences -> Mail & Newsgroups -> Mail Servers: Incoming Mail Servers
click Add if mhost.math.ias.edu is not shown in the window
(2)User's name and email address
Click Edit -> Preferences -> Mail & Newsgouprs -> Identity
(3) User's username for incoming email