[exim] Unrouteable address

Hi Guys

I have noticed a very weird problem, users using auto complete in
outlook are getting an error stating Unrouteable address.

When I look at the exim logs I see the following:

2008-07-15 11:04:30 [10644] 1KIgSU-0002lg-0Q Subject:
2008-07-15 11:04:30 [10644] 1KIgSU-0002lg-0Q <= ferozb@???
H=(cptisnmail01.korbitec.int) [10.4.2.10]:34397 I=[10.10.0.22]:25
P=esmtp S=1696 id=490F2
73F58BE854EBF3D5BE7CF7A8FC301E172B4@??? T="" from
<ferozb@???> for imran.allie@???
2008-07-15 11:04:32 [10645] 1KIgSU-0002lg-0Q **
imran.allie@??? F=<ferozb@???>: Unrouteable
address
2008-07-15 11:04:32 [10645] 1KIgSU-0002lg-0Q Completed QT=2s

I have checked the mail that they send and there is nothing funny about
the email address in the to field.

However when I ask them to not use auto complete and type the email
address in the address field, it works fine? Any ideas, this does not
happen to everyone, just some users lately.

Thanks for the help in advance
Peter