On Wed, 30 Jun 2004, Alan J. Flavell wrote:
> On Wed, 30 Jun 2004, Tony Finch wrote:
>
> > This can lead to email being silently lost.
>
> I would rate that as a client shortcoming, if it happens.
It's more subtle than that. If there is a problem with the user's
configuration this will often be detected immediately by their home
submission server and not by some ISP's port 25 interceptor. The message
will then double bounce -- the original message is rejected by your MX
and so is its bounce.
Real-life examples include the student who graduated and didn't
reconfigure his computer. When his account was disabled in mid-July his
messages sent from home started double bouncing. When Freeserve put their
port 25 interceptors into the RBL+, users who could previously send email
from home without reconfiguring found their email double bouncing.
In both cases the problem is accurately detected by requiring the MUA to
use TLS and AUTH, and is hidden if these are set optional.
Tony.
--
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http://dotat.at/
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