andras galos djdpsonetinformhu wietse venema wrote evidence hanging without reply would result different remote smtp client behavior sending 421 reply hanging im rather afraid 421 means try hangup says bad mx try another one chance fake reply shown sender instead real one real mx hangup compares better firewalled port 25 setup works well best regards andras galos wed 06 aug 2008 044058 0100 postfix fake mx