[Exim] Queueing / direct delivery (local)

Hi,

I run a small web community of about 250 users and every once in a while, I
send out a newsletter, from a PHP script. These are customised mails, so
there are 250 separate transactions to be done.

Before, when I used Exim 4.10, it took the script less than a minute to run
and all (or most) mails ended up in the queue, to be sent from there.

Recently, I upgraded to 4.14, but now the script takes over 9 minutes (!) to
run, and it seems every mail gets delivered immediately. The queue only
seems to end up with the few messages that couldn't be delivered right away.

This Exim 4.14 is compiled with Exiscan, but other than that, I didn't make
any changes to the configuration AFAICR. Now I can imagine that somehow
Exiscan (which is always run, even for locally generated messages like
these) could have this effect. Is that it, or did I just miss something or
screw something else up?

Thanks,
Martijn.