My OS: Ubuntu 9.04 server edition + DirectAdmin (Exim + Dovecot)

Having installed regular updates (aptitude update, aptitude safe-upgrade)
email are sent slowly with /usr/sbin/sendmail -t -i, which causes applications print PHP Mail errors even though emails are sent (but with delay as I suppose)
Updated Exim to the latest version, did not help.

Any suggestions are appreciated.