OT: How do you block servers sending oversize messages?

[Jim Holland]

This is a sendmail problem, but hope it's OK to ask here.

MANGO has only a 64k connection to the Internet.  We have a major problem 
with ISPs (mainly Yahoo and Gmail) that don't implement the SMTP SIZE 
extension.  So when they send us a 10 MB message, for example, we can't 
reject the message until they have sent us the whole message.  That is a 
total and serious waste of bandwidth, particularly when some idiot sends 
us half a dozen 10 MB bmp files for example.

On our side we can see the incoming df file growing in size in mqueue.in,
and can suspect from the sending server that it is going to be a problem,
but obviously can't be sure until it hits our message size limit (1.5 MB).  
At that point the df file stops increasing in size and we know it's a
problem.

The manual solution at that point is to determine the sender's IP address,
block that in the access file with an appropriate error message, kill the
process id associated with the connection and then delete the df file.  
Then wait until they next connect and get rejected, and then re-enable the
IP in the access file once more (and hope that they don't do it all over 
again).

The above response is definitely worth doing during our peak times as it
frees up significant bandwidth.  I could (why don't I?) write a script to
monitor and automate the process.  However the problem is fairly
fundamental, and I wonder if others are concerned about this issue and
whether they have solutions of their own.  

I have written to Gmail via a third party who knows the developers there
and am told they will think about it and possibly implement an upgrade at
some stage.  I don't know how to get hold of anyone interested at Yahoo.

Regards

Jim Holland
System Administrator
MANGO - Zimbabwe's non-profit e-mail service