[Exim] Uploading mailboxes

Hi,

I'm running into a very weird problem.

I want to upload some mailboxes to my internet server (remote) in order to
see them via webmail (my hosting provider offers me Neomail and Horde,
running on top of Exim).

I have two kind of mailboxes: those which messages have been downloaded by
Mozilla itself and those which messages were imported from Outlook 2003.
Both can be seen perfectly well inside Mozilla.

Since Mozilla uses mbox, I thought I could upload to my server in horder to
see my mail while on the road.

Now here's the weird thing:

If I upload the "native" Mozilla messages I can happily see them in my
webmail.

If I upload the imported-from-outlook mailboxes I cannot see them in my
webmail. I just see a big file, the "mbox" file, but not the individual
messages. (In the "from" column I'll see the mail hostname of the first
message in the file and in the "subject" column I'll see the path to the
file in the remote system).

First thing I tried was putting everything in a single mailbox, mixing
messages of the two types, but it didn't work: I either get the big file
with no visible messages or I can only see the "native" messages (yes even
when they're mixed with the imported ones in a single mbox).

I've tried to see the difference between the two types of mailboxes and it
seems the imported messages lack a few headers, that's it. Otherwise they
seem to be well-formed mbox files.

I've spent all this evening making all sorts of imports, exports, manual
tweaking of the files... everything, including searching the internet all
over, of course.

Any help will be very appreciated.

Thanks.

Pablo