Server Management > Network Services > Email > Blacklisting > Add / Modify

This form adds or edits one DNSBL used by the mail server. The list of services and the DNSBL block threshold live on the Email Server Settings — Blacklisting tab.

Enter the fully-qualified host name of the DNSBL, for example zen.spamhaus.org or bl.spamcop.net. Do not include http:// or a trailing path.

If enabled and the blacklist cannot be reached, the mail server returns a temporary error so the sending server will retry later. If disabled, mail is accepted when the list is unreachable. This is the Sendmail behaviour. Postfix/Postscreen does not use this option the same way.

Enable this DNSBL. Inactive entries stay in the GUI but are not queried.

Integer from 1 to 99. Default is 1.

When Postscreen queries this list and the connecting IP is listed, this weight is added to a score. Postscreen rejects the client only when that score is greater than or equal to the DNSBL block threshold on the Blacklisting tab.

Examples (Postfix/Postscreen):

• One list, weight 1, threshold 1 — any listing blocks (simple recommended setup).
• Three lists, each weight 1, threshold 2 — block only if at least two lists agree.
• A trusted list with weight 3 and threshold 3 — a hit on that list alone is enough, even if other lists are also enabled.

Save returns to the Blacklisting tab.