Re: dangers of email forgery

[Reindl Harald]

Am 30.03.2015 um 21:52 schrieb David F. Skoll:

On Mon, 30 Mar 2015 21:47:10 +0200
Reindl Harald <h.rei...@thelounge.net> wrote:

but i doubt that exchange don't know it's valid rcpt's and always
backscatters with no way to disable that behavior - even in case of
microsoft i doubt

Google specifically for Exchange 2013.  AFAIK, it's impossible in
general to get Exchange 2013 to reject a RCPT command to a nonexistent
user with a 5xx failure code.

And if you're filtering for customers on Office 365, there's
categorically no way to convince Microsoft that O365 should fail
invalid RCPT commmands

well, than you can't use recent MS Exchange as a MX and have to place a MTA in front which get it's user list via database, LDAP or whatever and is able to reject invalid RCPTs

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