Sunday, November 24, 2013

Domain Greylisting Issue

                                    Domain Greylisting

In This article, I am going to introduce you with a common issue of mail servers called Domain greylisting (emails are not getting deliver due to domain is greylisted in commtouch).

Issue: Emails were getting rejected due to domain was considering temporary as a Spam sender

Note: Greylisting is a measure against spam where the receiving server would reject a message temporarily with a message after which time to retry, usually within minutes and not later than some timeout (usually ~ 4 hours).  If the sender waits accordingly and resends the message within the timeout, it will be whitelisted, otherwise not.

How to check the domain greylisting

{Note: There is no exact tool to check the Greylisting of a domain, we can check the log files and NDR’s for more details.}

How to check domain whitelisting and blacklisting of domains.

Go to the following links and check.

Open this link and type the domain name under the Server Name or Domain and click on Blacklist check.
                             Image- 1.1

Note: For testing purpose here I am going to test the blacklisting of 

When you will type the under the domain name and click on blacklist check, you will get the following result.

                                    Image- 1.2

Note: Here you can see that this domain is showing blacklisted, it’s mean we are not able to send and receive emails from this domain, because it seems Spam sender.

How to verify that domain is whitelisting

Our email server doesn't seem to understand greylisting. When sending emails to external addresses whose servers implement greylisting, our MTA seems to retry several times immediately (which will be rejected for obvious reasons) and then give up and retry only after hours.

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