On Sat, 29 Jan 2005 21:45:20 GMT, raden wrote:

In message , Andy Hall
writes
- Bounce the message back after accepting it on the SMTP server.

- Reject it as undeliverable to the specific user by the SMTP server.

- Silently black hole.

Can someone explain exactly what black holing is

(apart from DIM^2's newly revealed fave pastime)

That doesn't bear thinking about, does it?


In the context of email, if you have your own SMTP server which you
manage yourself (or have appropriate access to a managed one), it is
usually set up to receive email for your domain. This might be
because it is permanently connected to the public Internet and a
domain name server is advertising its address as that to be used for
mail to your domain (using a DNS MX or mail exchanger) record; or
could be because your ISP initially receives mail for your domain but
forwards it to your SMTP server. Demon do this as an option to give
one example.

All of this is as opposed to a POP3 account at an ISP; where the ISP
handles the SMTP part.

So if you have said SMTP server or can manage one carrying your mail,
you can set rules for delivery with most software (e.g. sendmail,
postfix, etc.) One strategy is to bounce mail that doesn't match a
local mail user name. Another is to accept it and then silently throw
it away. In other words the difference between throwing the junk
mail in the bin as opposed to writing the address of the sender on it
and popping it into the postbox.

It disappears into a black hole.


A similar technique is used by some ISPs and carriers to handle one of
the other pains in the arse, the denial of service, or DOS attack (not
to be confused with Microsoft, although some would say that they are
similar in that they prevent doing anything useful).
There are various kinds of DOS attack, but a common one is for the
miscreant to use a large number of trojan/virus compromised PCs to
target a web site or other internet service and to swamp it with
various types of traffic or attempted access such that it becomes
unusable for legitimate users.
There are several ways to combat it, but a common one is for the
carrier/ISP to install a black holing router and to direct the traffic
to it for the duration of the attack rather than to allow it through
to the intended target. The black holing router simply silently
drops the DOS traffic. Depending on the type of attack, the miscreant
may not even know that this is being done.









--

..andy

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