UserGate Mail Server

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Connection Filtering

 
Connection filtering flow chart is shown in Fig. 1. When an incoming connection is registered on TCP port 25, UserGate Mail Server scans through its global white list of IP addresses. The white list is assigned on the “Antispam – Black and White Lists” page. Each list item may be an IP address (a range of IP addresses), a domain name (A-type record) or a name of domain mail exchanger (MX-type record). UserGate Mail Server resolves the listed names into corresponding IP addresses and generates global lists of resolved and restricted IP addresses. If the incoming connection originates from a white list IP address, UserGate Mail Server will skip all subsequent checks up until the rules created by the administrator and receive the message. UserGate Mail Server will block connection for IP addresses listed on the black list.
 
The next step is DNSBL check. If the incoming connection originates from an IP address that is on the spam list, UserGate Mail Server will reject and close the connection and generate a corresponding error message. You can set DNSBL parameters on the corresponding page of the administrator console. DNSBL parameters include names of DNSBL servers used in the check process and the exceptions list. Each exceptions list item may be represented by an IP address, domain name or name of mail exchanger.