[Mimedefang] Spam to inactive accounts

[Geoff Thornton]

I've been thinking along those lines as well for some time now.  My only
humble thought was that I would use a file, almost like a whitelist, to
store recipient names, whether the recipient is valid or not, plus a value
similar to a TTL that would allow caching of this information.  The names
and TTL values would be checked, added, deleted, or have their TTL values
renewed (for example, if their current TTL is half the original, then
re-check recipient and update values).  I was thinking that this would save
the effort of checking every recipient real-time, but also allow for
automatic updating of the recipients, without having to rely that the
destination server is always available.

My only dilemma is what to do to a message for a "new" recipient if the end
mail-server is unavailable.  I was thinking the best response was to send a
400 series 'message deferred' error to have the originating server to try
later.  Hopefully by the time the message retries, the end mail-server would
be available again.

Also, when I use the term TTL, I don't mean a numeric value that is
decremented each second, but a value like a future timestamp that indicates
when the information expires.  For example, newly added recipients could
start off with a future value like 8 days.  For the first 4 days, recipient
checks would be purely cached.  For the next 4 days, recipient checks would
be cached, but also include a request to the end mail-server to check for
that recipient.  If that recipient is still there, then the future timestamp
would be incremented by like 4 days.  If the recipient is not there, then
the recipient is immediately marked as invalid and the future timestamp
incremented by some amount.  After 8 days (or when the timestamp expires),
the information is purged from the file.

My thought is that would cache both valid and invalid recipient information
without holding stale records forever.  

Just my $.02


--Geoff Thornton


-----Original Message-----
From: jmiller at purifieddata.net [mailto:jmiller at purifieddata.net]
Sent: Thursday, October 17, 2002 1:16 AM
To: mimedefang at lists.roaringpenguin.com
Subject: Re: [Mimedefang] Spam to inactive accounts

>Since mimedefang is usually placed on a server that acts as a gateway to
>internal mail systems, and we now have the "filter_recipient" call in
>place, couldn't this problem be solved once and for all by a well designed
>filter_recipient function?

<snip>

>Please let me know if I'm totally off base here, or if anyone has any
>suggestions. I know there would have to be some workaround in place
>(for outgoing messages, as one example), but it strikes me as something
>that'd work really well if done right.
>
>If enough people are interested, (and multiple RCPT To:'s won't be an
>issue) I can throw something together, or maybe someone else would
>be interested in running with this idea.
>
>--
>Josh I.