is there a way i can stop sendmail to generate error reports, addressed to the sender, for mail messages which can't be delivered.
Probably the answer is yes, but you must not do that, or you'll break expected behaviour. If verifying addresses before or during sending wont work, and if you don't want to see those return messages add a recipe to the MDA's procmail to reroute those emails to a different user/mailbox. Of course you can deliver to mailbox /dev/null, but you'll forget that. Later on when "important" email is lost you've got no clue except reading the maillog.