[Exim] appendfile creating non-contigous data

I am using Exim 4.12. My local delivery transport looks like this
local_delivery:
driver = appendfile
delivery_date_add
envelope_to_add
file = /var/mail/$local_part
group = mail
mode = 0660
return_path_add
We have about 1100 users on our system. After about 1 month the ext3
filesystem get 80% non-contigous and the load soars with an average of
around 7. The performance suffers until I take the server offline and
archive to tape and recreate my ext3 partition and then read it all back
from tape. After which I am down to about 3% non-contigous. After
which it performs like a charm for awhile. I know appending to the
bottom of files is bad practice, but I dont know any other ways. Any
ideas I would appreciate greatly.

Thanks,
Joe Kezar