A 4.0 beta running on Solaris 2.5 is due this fall, and a final release is due in the first quarter of next year. A port to HP-UX is also planned, but no dates are available.
Microsoft officials acknowledged that the Version 3.0 code, which sources said was begun with the help of Bristol Technology Inc., was not up to par.
IE for Unix was first announced more than a year ago, but Microsoft officials said the company underestimated the difficulty of porting the application to Unix.
Meanwhile, Microsoft will post on Thursday an updated News and Mail client for Internet Explorer 3.02 for Windows 95.
The update contains tools to enable users to migrate messages and address books from Qualcomm Inc.'s Eudora Light, Eudora Pro or Netscape Communications Corp.'s Mail to IE's mail client.
The tools will be available today at Microsoft's Web site officials said.
Versions for Windows 3.11 and the Macintosh will be available in early summer, officials said.