Who is this hitting my server?

[Jason]

Hello,

I have two people/machines hitting my server looking for email. Neither user
exists...how can I find out who they are? No one at client's office seems to
know.

They are:
idontexist at validdomain.com
neitherdoi at validdomain.com

Also, I have a script that lives in a password protected directory. The
script uses php and overwrites a file owned by apache. The file being
written lives outside the pw protected dir. If apache owns it is it
relatively safe? It's a simple text file that needs to be viewable from
anyone in the outside world.

Thanks,

Jason