[exim] Exim and BCC Headers

Hey guys,

I'm sending a newsletter using PHP. I am using exim 4.63 in Debian Etch.
I do give exim roughly 17k email adresses as "Bcc:", but it does not
send out all the mails. I heard about an "Bcc:" limit, but couldn't find
such thing for exim.

Should I try to send batches of 500 "Bcc:" Headers ? And maybe put a
sleep between the calls?

Also I had a different idea and would like to know if this was possible:
Could I tell Exim to covert the "Bcc:" lines to actual "To:" lines? Or
could I give all the addresses as "To:" and tell exim to split them up?
The point of this is, that only one "To:" should appear in every mail,
but making a loop in php does not seem to be the best idea to do that!

Also, please don't point me to mailing list programs like mailman. I do
handle unsubscribing in myself and do have the mail addresses in my
database and do not want to incorporate them into mailman, since I would
have to keep 2 places synchronous.

Regards,
Samy