On Mon, 10 Feb 2014 07:08:38 +0100 (CET)
Steffen Kaiser skmimedef...@smail.inf.fh-bonn-rhein-sieg.de wrote:
what would be a good way to implement rate-limiting for outbound
mails per sender e.g. 50 recipients per smtp_auth sender per hour?
I do this in filter_begin. There I detect the sender, assign a
SenderID based on different rules and query a SQL database about
the sum of recipients of this SenderID in the last hour day. If the
SMTP quota is not exceeded, the tuple (scalar(@Recipients), SenderID,
NOW()) as added to the database.
Our CanIt product also implements rate-limiting, but we do it slightly
differently. We keep a table like this (PostgreSQLisms, sorry...)
CREATE TABLE sender_rate_limit (
sender TEXT PRIMARY KEY,
first_seen TIMESTAMP WITH TIME ZONE,
count INTEGER
);
Then when we see a RCPT from a sender (which can actually be an
envelope sender, the SMTP AUTH user, or the sending relay IP address)
we do the equivalent of:
BEGIN;
# Update existing bucket
UPDATE sender_rate_limit SET count = count + 1 WHERE sender = '$sender' AND
first_seen = now() - '1 hour'::interval;
# If the previous update did not update any rows, then:
# The next delete deletes a potential row where first_seen is
# more than one hour old
DELETE FROM sender_rate_limit WHERE sender = '$sender';
# And start a new bucket.
INSERT INTO sender_rate_limit(sender, first_seen, count) VALUES('$sender',
now(), 1);
COMMIT;
When it comes time to impose a rate limit, we can just do a:
SELECT count FROM sender_rate_limit WHERE sender = '$sender';
The lookups are very fast and don't require a SUM operation. The
downside is that it doesn't keep a running hourly sum, but resets
(more-or-less) once an hour so a sender can actually exceed the rate
limit for a while if the timing window is just right. In practice,
this has not been a problem.
Regards,
David.
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