> > It doesn't waste their resources, because it improves the level of > > service that they see. Giving someone immediate feedback that their > > address is invalid is far preferable to trying to send them a bounced > > mail message that will never arrive; and keeping our mail servers > > from being bogged down with bounces that will never get delivered > > helps free them up to deliver legitimate traffic. > > ... > > That is the same sort of reasoning that spammers use to justify > their activities. it's also the same sort of reasoning that you used to justify sending this mail to the IETF list. > - bounces would not bog down your mail servers, since you can discard > or otherwise deal with bounces with no more "bogging" than you are > spending poking at other people's systems. for a variety of reasons, that's simply not true for the cases where I'm using it. > (Many spammers want to receive bounces to clean their > lists, because some big ISPs and others automatically black-list > SMTP clients after they've sent to too many bad addresses.) perhaps, but even the spammers who clean their recipient lists don't necessarily use valid return addresses, and it's the return addresses that I'm checking. > - a mechanism that could really determine that addresses are valid > could be useful in a web page to provide immediate feedback to > users. The reality of MX servers, firewalls, sendmail "catch-all" > maps, and other things make the RCPT command too unreliable to use > for that purpose. BS. a simple syntax check isn't perfect either, but it's useful to catch some errors. this catches some more errors, without exhibiting false positives. it also has a cost, which is why I haven't recommended it for general use. but that doesn't mean it is useless. Keith