Hi Alex thanks for the on topic response. Bare with my thoughts.
> > - arbitrary valid email addresses are used as sender address by spammers > to avoid being blocking as unknown sender. Whenever one of your users > gets a spam mail, some innocent unknown user gets the "click on the > link" message by your mail system. It's not spammers are using always > their own usernames. Many spammers also use their spammer address > database as sender addresses as well. I think this argument cannot be used. Because when blocking a connection via rbl or so. The connection hosts gets the error code and message response and is and that host is generating the NDR not me. In my procedure the error code could have the message with the url. > - by sending the "click on the link" message you acknowledge to a > spammer some email he spammed is valid and not unknown. This is a kind > of information that should not be disclosed to spammers. No it does not. It also depends on when you invoke this check. Same again with an rbl check. The block is done even before headers are received. > - two persons who are both behind such a system are not able to > communicate to each other, because they never receive the "click on the > link" message. It is blocked by the other mail system and replied > automatically by another "click on the link" message. Both mail systems > are sending these messages endlessly to each other. It's the "chicken or > egg" problem. This is not true. Because mail servers should deliver these NDR's especially when it is one's own environment. > - "click on the link" messages are considered bad practice, because > users must not be educated to click on links in unexpected emails. >
