I think I’ve solved the problem…

What I did :

  • uninstall avast 4.5.536 + reboot + delete remaining files/directories
  • install avast 4.5.523 (the last official release) + avast automatically updates the vps to 0448-1
  • test with the eicar stuff : OK : no time delay to deal with the infected mail
  • I then restore avast parameters : silent mode + send alert mail on infection
  • reboot
  • test with aicar stuff : KO : long delay (3min.) to handle infected mail
  • I then removed the send alert mail on infection and everything run smooth again
    (all test using dialup connection)

Conclusion : It seems that the send alert mail is the problem…