Hello,
> Have a quick look to see if you have any entries in /var/log/maillog, or
> wherever sendmail would log things on your system.
>
> I thought I had the same problem once - turned out that there was another
> sendmail symlink somewhere which some program was calling, that still
> resolved to 'real' sendmail rather than exim.
that's it! I didn't remember the /usr/lib/sendmail link, but just
/usr/sbin/sendmail.