i've been running this relay gateway for 2 yrs now; i'd no problems of backscatters; have got a relay_recipient table and it take care of this; also kept a check on multiple bounces from an empty envelope sender;

this  particular scatter was for a customer domain and haven't kept recipient table for that domain since the customer is having their own mail server; in this situation where one has  got limited control on other mail server; my intention of post  was to know what other precautions can be taken on my gateway

thanks