SYMPTOMS

How to prevent a MailEnable server sending spam through mailbox redirections.  While the best method for preventing this issue is to prevent spam from entering the system in the first place, the setting outlined here will prevent the server forwarding messages that have already been classified as spam.

CAUSE

When a message is delivered to a mailbox that is redirected, the first action on the message by the post office connector is to redirect the message. This occurs before any other mailbox actions.  Because the message is immediately forwarded and the post office connector does not distinguish what folder the message is destined for (e.g. junk mail) - this means that all mail without exception is redirected.

SOLUTION

The solution to prevent the above behaviour occurring on redirections destined for the Junk E-Mail folder is to create the following registry key, and restart the postoffice connector service:

For 32bit servers:

[HKEY_LOCAL_MACHINE\SOFTWARE\Mail Enable\Mail Enable\Connectors\SF]
"Redirect Junk Mail"=dword:00000000

For 64bit servers:

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Mail Enable\Mail Enable\Connectors\SF]
"Redirect Junk Mail"=dword:00000000