OpenBSD's spamd.

Christopher Hilton chris at
Tue Dec 19 09:05:29 PST 2006

Oliver Fromme wrote:
> Dimitry Andric wrote:
>  > Oliver Fromme wrote:
>  > > What does stuttering mean?  Is it similar to sendmail's
>  > > "greet_pause" feature?
>  > 
>  > See here:
>  >
> OK, so the answer to my question seems to be "yes".  :-)

Actually I'd say it's similar. If you telnet to port 25 on a server 
that's using sendmail's greet_pause option I'm assuming that you get 
nothing for 5 seconds. OpenSD's Spamd sends the initial greeting at a 
rate of one character per second and only accepts data from you at the 
same rate.

Through experimentation Bob Beck determined that many spammers were 
dropping the connection and forgetting about delivering the mail 
completely after short and shorter intervals if the connection was rate 
limited to 1 character / sec. When the spammers got down to 3 seconds he 
modified spamd to stutter for 10 seconds on any connection. That feature 
came in on OpenBSD 3.8

-- Chris

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