Greylisting has proven itself to be an effective method
of spam prevention. It works by returning a temporary failure to all
unknown incoming messages. Valid servers will retry the email a short
time later, which would be permitted. Spam scripts, however, rarely
retry on temporary failures. Emails from Trusted Senders and White
listed IP addresses will automatically bypass Greylisting and are
delivered directly to the Spool.
The premise is that Spammers create scripts that bombard your server
with emails. These messages are then bounced back to their sending email
server. Since, most spam does not come from valid email servers, the
messages are not retried and therefore this reduces the amount of spam
that your customers receive.
For those messages that are sent from valid email servers, the sending
server should retry at least four times. If the first retry is beyond
the Block period (default 15 minutes) and within the Pass Period
(default 6 hours) the message is passed to the Spool and it goes through
its normal processing. A record is also created that says this is a
valid email address and keeps it for 36 days (default). If another email
from the same email address is received within the 36 days, the clock
is reset for an additional 36 days and delivered directly to the Spool.
To enable Greylisting:
- Login into the SmarterMail web interface as the System Administrator
- Click the Security icon.
- Click on Greylisting.
- Click Enable Greylisting checkbox
- Click Save.
Article ID: 13, Created On: 6/20/2011, Modified: 6/20/2011