Distribution lists in E2K

I have user eg: Fred Bloggs who is in AD/E2K and a members of a dist listin Ad/E2K. He is using that same dist list to mail out. All messages deliver ok, but as well as recieveing the expected mail he also recieves a sys admin message –
The following recipient(s) could not be reached:
Fred Bloggs on
The recipient has been deleted or has no e-mail address.

Any Ideas…..