[cobalt-users] Raq3, bulk emailing and a lame DoS

["Per Magne Knutsen" <pknutsen@xxxxxxxxx>]

I'm sending out a newsletter to about 4000 subscribers or so, using a PC
based software called WorldMerge. I'm using the software (rather than
majordomo) as I require "personalization" of the messages. Messages are
sent out one by one. However, after about each 250-270 emails or so, the
email server falls down and the Raq emails me (the admin) the error
message:

*****
The SMTP (mail) server appears to be down.  The mail server may shut itself
down temporarily under extreme load, so you should also check the CPU load
on the server...  blah, blah...
****

I cannot mail more messages, neither from WorldMerge nor Outlook (socket
errors: 10061 and 10022). The problem corrects itself after about 10
minutes, but forces me start to from the beginning with a 'cropped'
recipients-list. Very annoying.  Next time I'll write a script for this
job, although that won't change much with regard to the load produced.

I have difficulties believing that the server could be under 'extreme'
load, as WoldMerge only sends out a message every 2-3 seconds or so (I'm
working remotely via a dial-up). When I look at top, sendmail never has
more than a few threads open using about 0.1% CPU each.

Does anyone know why this DoS occurs and what can be done to prevent it?


Thanks,
Per M
nethut.no