This is the Postfix 3.1 (experimental) release. The stable Postfix release is called postfix-3.0.x where 3=major release number, 0=minor release number, x=patchlevel. The stable release never changes except for patches that address bugs or emergencies. Patches change the patchlevel and the release date. New features are developed in snapshot releases. These are called postfix-3.1-yyyymmdd where yyyymmdd is the release date (yyyy=year, mm=month, dd=day). Patches are never issued for snapshot releases; instead, a new snapshot is released. The mail_release_date configuration parameter (format: yyyymmdd) specifies the release date of a stable release or snapshot release. If you upgrade from Postfix 2.11 or earlier, read RELEASE_NOTES-3.0 before proceeding. Major change with snaphot 20106XX postscreen support for the TTL of DNS lookup results, including TTLs of "not found" results (as described in RFC 2308). Historically, the default setting "postscreen_dnsbl_ttl = 1h" assumes that a "not found" result from a DNSBL server will be valid for one hour. This may have been adequate five years ago, but nowadays, this will result in missed opportunities to block spambots. Support for DNS reply TTL values is controlled by two parameters: postscreen_dnsbl_ttl_minimum (default: 1 minute). This parameter specifies a minimum for the amount of time that a result will be cached in the postscreen_cache_map. This prevents an excessive number of postscreen cache updates when a DNSBNL or DNSWL server specifies a very small reply TTL. The postscreen_dnsbl_ttl (default: 1 hour) This parameter already exists. It now specifies an upper bound for for the amount of time that a result will be cached in the postscreen_cache_map. This prevents cache pollution when a DNSBNL or DNSWL server specifies a very large replt TTL.