mutt dont separate mails processed by procmail

[Dumas Patrice]

Hi,

I use procmail to filtrate my mails, but they are not correctly displayed. They
are viewed concatenated by mutt in a single big mail. Or mutt says it isn't a
valid mailbox. 

Is it something known ? It seems strange to me
because I thought a lot of people used mutt and procmail... 
My first thoughht is that I have a bad config of something, but of what ?

Here are the versions of the softwares I use :
procmail v3.14
Mutt 1.2.5i

I use standard unix mailboxes.

Thanks in advance

Pat