amavisd and Avast! scanner - permission problems

[Jakob Curdes]

Hi, we try to use the Avast! scanner with amavisd. There are a couple of 
scanner definitions out there, but regardless whether we use

  ['AVAST Antivirus - Client/Server Version', '/bin/scan',
  '{}', [0], [1],
  qr/\t(.+)/m ],

or

  ['avast! Antivirus daemon',
    \&ask_daemon,       # greets with 220, terminate with QUIT
    ["SCAN {}\015\012QUIT\015\012", '/var/run/avast/scan.sock'],
    qr/\t\[\+\]/, qr/\t\[L\]\t/, qr/\t\[L\]\t([^[ \t\015\012]+)/ ],


we always get the following permission errors:

Jun  2 12:54:42 comm amavis[27447]: (27447-01) run_av Using (AVAST 
Antivirus - Client/Server Version): /bin/scan 
/var/spool/amavisd/tmp/amavis-20140602T125442-27447-6dIAWWfA/parts
Jun  2 12:54:42 comm amavis[27447]: (27447-01) run_av: /bin/scan exit 2, 
avast: 
/var/spool/amavisd/tmp/amavis-20140602T125442-27447-6dIAWWfA/parts: 
Permission denied
Jun  2 12:54:42 comm amavis[27447]: (27447-01) (!)run_av (AVAST 
Antivirus - Client/Server Version) FAILED - unexpected exit 2, 
output="avast: 
/var/spool/amavisd/tmp/amavis-20140602T125442-27447-6dIAWWfA/parts: 
Permission denied"
Jun  2 12:54:42 comm amavis[27447]: (27447-01) (!)AVAST Antivirus - 
Client/Server Version av-scanner FAILED: /bin/scan unexpected exit 2, 
output="avast: 
/var/spool/amavisd/tmp/amavis-20140602T125442-27447-6dIAWWfA/parts: 
Permission denied" at (eval 103) line 897.

The Avast processes run under the user avast which is member of the 
amavis group. But this seems not to be enough? It seems that there is no 
option to have the avast processes run as user amavis, so we need to fix 
the permissions.

Maybe other avast users can recommend a setup !?

Regards,
Jakob Curdes