[Exim] How big can a mail file be??

Now that I have it so every message will forward to one box I need to know
how big that mail file can be and what I should read it with.

I expect 5-10 thousand message. I basicall just need to have a way to count
them and look at a couple of them to verify that they have the correct
content. Any suggestion on what reader can do that??

Thanks

Keith
kpettit@???