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The Greylisting method is very simple. It only looks at three pieces of information (which is refer to as a "triplet") about any particular mail delivery attempt:
The IP address of the host attempting the delivery.
The envelope sender address.
The envelope recipient address.
Greylisting follows the basic rule which is:
If we have never seen this triplet before, then refuse this delivery and any others that may come within a certain period of time with a temporary failure.
Before applying greylisting procedure ITASM performs following filter checks on incomming emails.
Perform blacklist check. Blocks email if IP is blacklisted and skip greylisting.
Perform whistelist check. Allow email if IP is whitelisted and skip greylisting.
Apply header filter to the recipient of emails. If score encountered is -ve then email is allowed else if score is +ve email is blocked.
Apply sender filter to the sender of email. If sender score is found -ve then greylist will be bypassed. If sender history is maintained and score assigned by sender history is -ve then also greylist will be bypassed.
For more information read the following whitepaper Greylisting by Evan Harris
GreyListing is bypassed when the user is authenticated and "Bypass authenticated users" option is enabled.
Enable GreyList: Uncheck this box if you do not want to use Grey List feature
View Grey List Records
Manage Grey List
INITIAL DELAY (SECONDS): Initial delay is the blocking time period after which same email will be allowed to start smtp conversaton.
DELAY AGING TIME (SECONDS): This is the time window for email to go through if it retry with in this time period.
WHITE LIST AGING TIME (SECONDS): This is the time period the white list record will remain valid.
UNIT CONVERSION: 1 min = 60 Seconds
1 hr = 3600 seconds
1 Day = 86400 seconds
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