mail.app question

[Wilhelm Wanders]

hi list ^_^

i set up my mail.app to redirect all mail from this list in a mailbox 
called TiBook List. It works just great this way, but about every 4-6 
weeks following is happening:
i usually keep the posts with interesting topics remaining where they 
are (in the TiBook mailbox that is - sorted by date always the new ones 
on top)
every 4-6 weeks mail.app starts up and selects all old messages as new 
(in this mailbox). this is not that big of a deal, but maybe someone 
else experienced this yet ?
any input is, as always appreciated

^_^