The messages are from your real watchDirectory tasks (wdPostMan doesn't create messages, it just sends them for the watchDirectory tasks).
watchDirectory "gives" wdPostMan work by writing messages to the directory
Code:C:\Documents and Settings\All Users\Application Data\watchDirectory\System.Mail\Out
wdPostMan noticed the new file and sends it as an email.
If sending the email fails it will be placed in the directory
Code:C:\Documents and Settings\All Users\Application Data\watchDirectory\System.Mail\fail
And from there, the sending will be retried a few times (depending on your settings).
There are probably several *.wdmail files inside your "System.Mail\out" and/or "System.Mail\fail" directory written by previous runs of your tasks that are still waiting to be sent...
Does that make any sense?
Gert