[exim] incoming message lost

hi all,
I'm running exim 4.60 without problems for months.
In the last month I have a seriuos problems.
Message incoming from some domains get totally losted without any error sent
back to sender.
Exim is installed with Spamassassin and MailScanner

In the debug I get:
14614 SMTP>> 421 mail.XXXXXXXXXXX.it lost input connection^M
14614 LOG: smtp_connection MAIN
14614 SMTP connection from cp-out4.libero.it [212.52.84.104] lost
14614 search_tidyup called

thanks
--
Francesco Pasqualini