Milter-greylist

Emmanuel Dreyfus wrote:
> On Wed, Aug 08, 2007 at 09:44:03AM -0700, Simon Gao wrote:
>> Will this work for subject line also, like following?
>> acl greylist subject /^<>$/ delay 6m autowhite 5d
> 
> We don't have this clause. You can filter on the headers (note it's dacl:
> DATA stage):
> dacl whitelist header /^Subject: <>$/

Also, you'd want to drop the <> part.. that won't appear in a normal subject line.

Something like this might work better:
/^Subject:( )*$/

Which will match subject lines that are empty, or those containing spaces.

> 
> I don't recall if we can greylist at data stage, thought. I suspect we
> can't

I think you can, but you get restricted to greylisting all recipients of the
email. ie: no whitelists.
However, even if it is possibl, greylisting at the data stage is unwise as it
could be hazardous to your bandwidth. You're essentially tempfail'ing the
message after the whole message has been transmitted. If the sending server
retries often, and the message is large, you'll consume a lot of bandwidth.

(And for reference, it is IMPOSSIBLE to greylist after the subject, or any other
header, but before the body. There's no pause in the SMTP protocol there, so the
server can't return a 4xx error code until it is all done. To the SMTP protocol,
the headers and body are all one piece, they are just the DATA.)