BANNER PURGE DELAY

TCP/IP-channel-specific options: BANNER_PURGE_DELAY (integer)
(New in MS 6.3.) A useful spam-fighting strategy is to delay sending the SMTP banner for a brief time (half a second, say), then  clear the input buffer, and finally send the banner. The reason this works is that many spam clients are not standards-compliant and start  blasting SMTP commands as soon as the connection is open. Spam clients that do this when this capability is enabled will lose the first few  commands in the SMTP dialogue, rendering the remainder of the dialogue  invalid.

The  SMTP server option exists to implement  this strategy. Set the  option to the number of  centiseconds to delay before purging the input buffer and sending the  banner. The default value of 0 disables both the delay and purge. See also the PORT_ACCESS mapping table   flag, which can also be used to set such a banner  purge delay, in a more selective manner And note that the    channel  option may be of interest when using any such banner purge  delay technique.

See also:
 * PORT_ACCESS mapping table
 * disconnectbadcommandlimit Option
 * TCPIP-channel-specific options