Re: [ietf-smtp] DSNs

[Sam Varshavchik <[e-mail]>]

John Levine writes:

> With SMTP you have no way to tell who is sending a message that
> arrives from outside, and experience tells us that the majority of
> incoming mail is hostile.  We don't do success notifications or web
> bugs because we don't want to leak info about our users to malicious
> strangers.

Can someone explain something, slowly, to me:

Incoming mail is addressed to a non-existent recipient. Your MTA rejects the  
recipient.

Incoming mail is addressed to a valid mailbox. Your MTA accepts it. As such,  
the sender already knows it is a valid recipient.

I don't follow what information is getting leaked, if a second later a  
success DSN gets sent to the sender. The sender already knows it's a valid  
mailbox, by the virtue of the fact that the mail was accepted.