[imp] link attachments & VFS

[Andreas Moroder]

Hello,

is there documentation that explains what exactly link attachments & VFS 
in imp do ?

Is it possible to configure IMP to send the link when the user is in the 
same domain and attach the file when the user has another domain ?
What if some users in the domain use fat clients ?

IS the attachment only stored once ? What if the sender deletes the mail 
from the outbox ?

Thanks
Andreas