Quoting Oscar del Rio <del...@mie.utoronto.ca>:
On 05/13/14 03:02 PM, Stephan Bosch wrote:
Use of NULL envelope sender is generally recommended to prevent mail
loops
Unfortunately, many servers out there reject emails with NULL sender.
Some recent examples (real server names edited) :
Any domain hosted by RackSpace will reject a NULL sender for
'backscatter'.
Bascially, 'backscatter' blockers assume all edge SMTP servers will have
complete knowledge of the final delivery status - during the SMTP
conversation - thus labeling all NULL senders as forged spam redirected to
them via a bounce message.
http://www.backscatterer.org/
Rick
