Reply to ticket by emai

Sorry. may be double (first message has wrong From: address)
Hi all.
User can create ticket by email. When i’m sending them an answer and
then user answer to my answer :wink: system doesn’t allow to post it:

RT thinks this message may be a bounce
Permission Denied (/usr/lib/rt/RT/Interface/

I’ve latest rt-3.4.2+svn updates.
User must have login to do such things?