How I can configure my local mail delivery daemon (sendmail or postfix) to
use my isp's smtp server when the amount of data to be sent is too big?
i.e. I want to use my local mail delivery daemon always, BUT if some user
on my system sends a BIG email to many recipients it is delivered using my
isp's smtp server in order to not repeat the upload data... This can be
configured in sendmail or postfix transparent to the users?