Log Message:
Changes 2.6.4:
Bug Fixes
* amavisd failed to start when spam scanning was disabled either
  by @bypass_spam_checks_maps=(1) or by @spam_scanners=(), giving:
    Can't locate object method "new" via package \ 
"Amavis::SpamControl"
  As a workaround one could use a @spam_scanners=(undef) to disable spam
  scanning;
* several decoders failed to propagate "Exceeded storage quota" exception,
  so the protection of AV scanners against mail bombs was ineffective;
  reported by Jorgen Lundman;
* milter usage (AM.PDP): verbatim header edits inserted a header body of
  "1" instead of the correct string
* updated AV entry for BitDefender's bdscan to recognize tabs around
  a colon in its output; contributed by Steve;
* fix parsing of a combined result from DSPAM (option --classify), as
  earlier versions of DSPAM did not include a signature with a combined
  result line; problem reported by Marijan Vidmar;
New Features
* provide a true SNMP agent and a MIB, facilitating monitoring the health
  of a content filtering system, its performance and mail characteristics;
* a new AV interface to SMTP-based antivirus scanners;
* allow customizing SMTP-status response reason text for blocked messages;
* prevent inserting fake copies of certain important mail header fields
  without breaking a DKIM signature;