The mailing list for listmasters using Sympa

["Thomas Barth" <address@concealed>]

Hi,
when I send an email to an address that is included
in /etc/aliases (sympa: "|/home/sympa/bin/queue address@concealed"),
sympa simply put the email into the spool subdirectory msg/bad.
(e.g. address@concealed) 
What is done next to send this file/email to the recipient?
Why does sympa use the msg/bad-directory?

Thomas B.