You really should send NDR's, otherwise geniune emails that are wrongly detected may 'go missing'.

It isn't SF that actually generates the NDR, SF simply refuses to accept the incomming email which causes the sending server to generate and deliver the NDR.

I think SF only generates an NDR if it has issues delivering an email it has already accepted to the destination server, either user does not exist or other server problems.

If you get a lot of spam going to unknown users I would recommend you implement the AuthorizedTo filter - I've seen a dramatic decrease in the quarantine size since going this and a lot of emails being blocked!


Edited by lyndonje