[exim] Problem with exim an phpmailer

Hello,

i´m running debian sarge with exim 4.34 and apache2. we have a php script which
read all the emailaddress from a mysql und send the email with the phpmailer.the
exim is running local. we send about 5000 emails. this works fine. but from time
to time(sometime 1 hour sometimes 2 month) the sending of email failed. the
phpmailer writes every 30 sec in the logfile that he can not give the exim the
email. if we stopp the exim and delete all the files in the spool directory and
start the exim again it works.
the emails are each time the same. we gave the emails via smtp to the exim.

thx

kai