[SM-USERS] Not sending email

[godart]

Hello everyone,
 
The Squirrel webmail, that I installed on my server, always worked well but suddenly gives me a big problem : email that I send is copied in the "sent" folder, as if it was sent, but it is *not* sent ... And I never receive a failure notice or anything similar. Of course that is a serious problem as I think people have read from me and they have not.
 
Can anyone help me to find out why mail is not sent even though it is copied in the sent folder ?
 
By advance, thank you.
 
Best regards from Belgium,
 
Jean-Marc