Thomas POINDESSOUS: > > Hi, > > I have a problem between one of my postfix and a zimbra server (postfix > server). > > sometime (one mail every three days), I got this error : > 502 5.5.2 Error: command not recognized (in reply to RCPT TO command) > > I did a tcpdump to understand why I got this error and I found > that one of the "RCPT TO:" command is cut in two packets.
This often happens with "firewall" products that inspect the TCP stream. In particular, CISCO has a reputation of breaking SMTP by mis-handling commands, including commands that sit on a packet boundary. If there is a CISCO firewall in the path, issue the proper commands to disable SMTP inspection (whatever they call it today). You can also selectively disable ESMTP command pipelining. See: http://www.postfix.org/postconf.5.html#smtp_discard_ehlo_keywords http://www.postfix.org/postconf.5.html#smtp_discard_ehlo_keyword_address_maps The keyword in question is "pipelining". Using this will reduce mail delivery performance, so you may not want to turn it on for all mail. Wietse
