Exception for Greylisting by geo location (countries)

Hi,

You cannot explicitly define country blocking with GreyListing feature, but you can use the country blocking for specific services (here- SMTP, POP and IMAP).

Thanks

Hi sachingurung,

thanks for your reply. Too bad, that this feature doesn't exists. Could you clarify the following line under under "Email Protection" -> "SMTP" -> "AntiSpam" -> "Advanced anti-spam features":

Greylisting builds and uses a database of ’known-good’ SMTP hosts that resend messages after receiving a temporary error

Does this mean that Mail Server, which successfully resend mails after a "greylisting bounce" are no longer greylisted (so mails from theese servers are no longer bounced)

Greetings

Alex

Hi sachingurung,

thanks for your reply. Too bad, that this feature doesn't exists. Could you clarify the following line under under "Email Protection" -> "SMTP" -> "AntiSpam" -> "Advanced anti-spam features":

Greylisting builds and uses a database of ’known-good’ SMTP hosts that resend messages after receiving a temporary error

Does this mean that Mail Server, which successfully resend mails after a "greylisting bounce" are no longer greylisted (so mails from theese servers are no longer bounced)

Greetings

Alex

Hi Alex,

Greylisting uses the fact that most senders of spam messages use software based on the "fire-and-forget" method: Try to deliver the mail and if it doesn’t work, forget it! This means that senders of spam mail do not try to send emails again when there is a temporary failure. The assumption is that since temporary failures are built into the RFC specifications for email delivery, a legitimate server will try again to send the email later, at which time the destination will accept it. Hence, once the server resends a mail it will be sent successfully. 

You can raise the country blocking feature associated with grey-listing here.

Thanks

Problem is:

1. with greylisting - all emails are greylisted. They continue to be greylisted which can cause a delay

2. Country blocking with smtp - does what it says on the tin. problem is, you don't know where the mail server will be and if it's in one of the blocked countries, you are screwed. You could keep putting exceptions in constantly.

The UTM would be far better that when it sent to somewhere, it could ignore the country blocking and allow 10s for the the remote MTA to do an rDNS lookup.

Sachin's information is exactly correct, but I'm with Louis in recommending against both Greylisting and Country Blocking for what you want to accomplish.

In fact, without using Greylisting, only about 1% of emails received by the UTM will be quarantined, and most of those represent legitimate senders where your recipient doesn't recall asking to be on a mailing list.  These would not be blocked by Greylisting, and only a small portion of the others would.

Of the emails not delivered to your users, 96% will be stopped by, in order of importance: rDNS, RBLs, "No such recipient," SPF & BATV.  These checks all occur at SMTP time, so the complete headers and content of the message are never received.  I guess that, as far as the load on your UTM and the volume of SMTP traffic received is concerned, there's no net savings with Greylisting, so all emails are slowed down for no net gain of resources.  Of the total of emails actually received and scanned for Anti-Virus and Anti-Spam, about 90% are delivered to your users and two thirds of the rest get rejected.  Again, this is all without Greylisting active.

Cheers - Bob