UserGate Mail Server

  Administrator's Manual


Recipient Filtering

UserGate Mail Server starts recipient filtering after the RCPT TO command has been received. The received address is checked against the black and white lists. If the destination address is found in the white list, all subsequent checks will be skipped. If the address is found on the black list, UserGate Mail Server will close the incoming connection and produce a corresponding error message.
Next, UserGate Mail Server checks the availability of the destination address in accordance with the mail domains (“Communication Server – Domains” page). If destination domain is remote domain, then UserGate Mail Server connects to the mail server specified in the route and requests the availability of the recipient by sending the RCPT TO command. If the mail server contains no such recipient address, UserGate Mail Server will produce a corresponding error message.
For each incoming connection, UserGate Mail Server creates a triplet (IP address originating the connection, MAIL FROM address and RCPT TO address) and scans the internal list of triplets for previous connections. If the received triplet is not found in the internal triplet list (i.e. the connection with the given parameters is a new connection), UserGate Mail Server will produce a temporary error message. This is a Greylisting check procedure. You can set the Greylisting parameters in the Antispam section of the corresponding Greylisting page.
UserGate Mail Server supports the Tarpiting feature to protect you from address guessing. The Tarpiting feature “delays” mail server response when a new destination address is received in the RCPT TO command. By default, response delay will be enabled if more than five destination addresses are received at once. You can set the required Tarpiting parameters on the “Antispam – Settings” page.