Greylisting Security Measures for Mail Transfers

Nagoya University started using greylisting security measures for the Nagoya University Mail Server on June 27, 2005, and the previous host-authentication security measures were discontinued.

The greylisting method suspends email reception temporarily from a mail server that is not registered on the database as a provisional error.

If a mail server detects a provisional error, the originating mail server regularly tries to　send the mail again for a specified period. When the mail is sent again after 15 minutes or more, the destination server will receive it.

This greylisting method contains the following problems:

1. IT MAY CAUSE A 15 MINUTE OR LONGER DELAY IN RECEIVING EMAIL.

Although you are told on the phone that email has just been sent, you may only receive 15 minutes or more later. In addition, the mail sending timing depends on the server configuration so that the delay in mail arrival may be one hour or more in some cases.

2. SOME ORIGINATING SERVERS MAY NOT TREAT PROVISIONAL ERRORS APPROPRIATELY DUE TO THEIR CONFIGURATION.

In particular, when using email to send acceptance information on a web page to accept participation in an academic conference, etc. and the CGI program on the web page does not correspond to the provisional error, the email may not be delivered.

If you do not receive email that should have been delivered, please contact the email server administrator via email at hostmaster@nagoya-u.ac.jp.

EFFECTS OF ELIMINATING SPAM BY HOST-AUTHENTICATION AND GREYLISTING METHODS.

Status of receiving spam with a spam monitoring address