Redalto Communications Support Site
Question: What is Greylisting?
This question relates to category Email
Answer:
Greylisting (or graylisting) is a method of defending e-mail users against spam. Redalto uses grey listing as one of many tools to block inbound spam.
How does it work?
Mail servers using greylisting will "temporarily reject" any email from a sender it does not recognise (ie, the first time an email is received from a specific domain). If the mail is legitimate, the originating mail server will after a delay try again (defined by sending server), and if sufficient time has elapsed, the email will be accepted. If the mail is from a spammer it will probably not be retried since a spammer goes through thousands of email addresses and typically cannot afford the time delay to retry.
The Methodology behind Greylisting
Greylisting is effective because many mass email tools used by spammers will not bother to retry a failed delivery, so the spam is never delivered. A spam sender may retry with a different sender, and possibly a different message, because it has a queue of victims rather than the proper queue of messages that regular mail servers maintain.
In addition, if a spammer does retry a delivery after the waiting period has expired, any one of a number of automated spamtraps will have had a good chance of identifying the spam source and listing both the source and the particular message in their databases. Thus, these subsequent attempts are more likely to be detected as spam by other mechanisms than they were before the greylisting delay.
How does it work?
Mail servers using greylisting will "temporarily reject" any email from a sender it does not recognise (ie, the first time an email is received from a specific domain). If the mail is legitimate, the originating mail server will after a delay try again (defined by sending server), and if sufficient time has elapsed, the email will be accepted. If the mail is from a spammer it will probably not be retried since a spammer goes through thousands of email addresses and typically cannot afford the time delay to retry.
The Methodology behind Greylisting
Greylisting is effective because many mass email tools used by spammers will not bother to retry a failed delivery, so the spam is never delivered. A spam sender may retry with a different sender, and possibly a different message, because it has a queue of victims rather than the proper queue of messages that regular mail servers maintain.
In addition, if a spammer does retry a delivery after the waiting period has expired, any one of a number of automated spamtraps will have had a good chance of identifying the spam source and listing both the source and the particular message in their databases. Thus, these subsequent attempts are more likely to be detected as spam by other mechanisms than they were before the greylisting delay.
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- Author: Redalto Support Team
- Created on: 10 Mar 2010
- Views: 1230
- Last modified: 10 Mar 2010
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