Grey List temp fail - what does this mean?

[david]

Hi there,

If I understand correctly this log record (from SMTP server log) means that the sender is temporary blocked and the sending server gets notified to try again soon, right?

For some reason those emails don't come through even after several hours.

Am I missing anything here? Is there anything else I should check?

(I am using latest AMS on Win2003 server).

Thanks!

[Code Crafters]

Let me explain how grey listing works. An email from an unknown IP is given a temporary failure message as if the mail server is unavailable and please try again soon. The sending client / mail server should then retry and delivery will be accepted within the grey listing window (default 1-3 hours later). Once accepted within this window the IP is white listed and not temp failed again.

This filter is very effective and will often stop 80% of all SPAM on its own. It filters out mail from SPAM clients which generally try once and then give up for a while. Proper sending mail servers will retry for many hours and will generally always be accepted. Obviously the default wait time of 1 hour means an delay in your mail delivery so you can change this 60 minute default to 1 or 5 minutes to reduce the delay without comprimising the effectiveness of the filter too much.

Clients sending directly to the mail server obviously can't retry as easily as another mail server can but you can use the relaying exemption and white listing options to allow clients that have logged into their mail client for outgoing mail relaying access to the mail server or who are white listed to skip all SPAM filtering and avoid this problem since they are already pre-authenticated.

[sillyme]

Correct me if I am wrong but grey list also relys on the senders email and server address as a pair for the first approval. Check the log file for the originating IP address. I have found some cases where the senders mail keeps moving from server to server (farm I guess). A few also just send once. These I just add to the white list.

[Code Crafters]

Actually, you are right. The identification of a grey listed sender is based on the SMTP envelope sender, SMTP envelope recipients and sender IP. All of these define a unique record for greater accuracy.