Why I think RBL should be done with the MTA rather than Mailscann er

Patterson S.R. S.R.Patterson at SOTON.AC.UK
Tue Jun 25 10:13:07 IST 2002

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I'm just working through in my head the options for spam blocking and
come up with the following advantages to using RBL lists on the MTA
(i.e. sendmail) at point of acceptance rather than using them on

- - Reduced server load - you don't have to bother accepting a mail
for delivery (i.e. spooling it all up) when you already know you're
going to reject it anyway

- - The remote user/server gets a sensible rejection message at the
point of "MAIL FROM:" or "RCPT TO:" along the lines of "Your domain is
black listed, please see http://useful.url"

- - Perhaps of maximum importance to me, you have complete control of
your mail relaying policies through sendmail itself - for example, I
want to use the MAPS Dial up list to block direct mailing to my
servers from diaul up users.  However, I don't want to stop valid
University users at home on their dialup connections from sending mail
through my servers.  The answer - implement SMTP Authentication
(already done!) and only reject IP addresses in the MAPS Dial Up list
if the user hasn't first authenticated themselves with a valid
username and password.  How would you do this in Mailscanner?

Can anybody see any advantages to using the RBL lists on Mailscanner
instead of on the MTA directly?  I'd like to hear the flip side of the

This is by no means a dig at the product or at Julian who works very
hard to implement all of the features which his userbase demands
(though I somethimes think the userbase demands inappropriate
features... Don't even get me started on SA...;P)

Here's a feature for you Jules... How about making "plug in" module
support for each MTA, spam features, Spam Assassin, Virus scanner, etc
- by which I mean you only load the code which you need for the
features and software that you are using.  No, don't ask me how you'd
do that :)

Yours ramblingly, Steve
- --
Steven Patterson, MSci.  Tel: +44 (0)2380 595810
Electronic Information Systems Support and Development
Computing Services, University of Southampton, UK.
Public PGP Key: http://www.soton.ac.uk/~srp/pubkey.asc

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