Thanks, as always, for Postfix! I have been using it for at least ten years what I describe below is the first time I have questioned how well it works. This is version 2.3.3 on CentOS 5.1.
When Postfix (or any other MTA) attempts to send a message to another MTA, and that remote MTA rejects the message, with a 544 code, I understand that the first MTA is supposed to report the error with a message to the sender. Postfix does this, but the way it formats the error message text sent by the remote MTA may not be correct. I am not sure whether this is specified in an RFC, but I understand that for every part of the remote MTA's response which starts with "544-" there should be a new line in the message to the sender. This behaviour is relied upon by at least one spam rejection system, in order that the sender gets a nicely formatted explanation and instructions on how to have the message delivered. This software is Karl Denninger's Spamblock-Sys: http://www.denninger.net/spamblock.htm It rejects every message with a sender address which the system does not yet recognise. Sending a message to k...@denninger.net will generate such an error response, unless of course the sender address is already recognised. Below is the first part of the error message generated by Yahoo's qmail, which is formatted as Karl intends it to be: = = = = = = = = = Hi. This is the qmail-send program at yahoo.com. I'm afraid I wasn't able to deliver your message to the following addresses. This is a permanent error; I've given up. Sorry it didn't work out. <k...@denninger.net>: 70.169.168.7 failed after I sent the message. Remote host said: 554-Subject: SUSPECTED Spam QUARRANTINED - please read for further information 554- 554-The SPAMBLOCK-SYS spam protection system has QUARRANTINED your 554-message to the following user: 554-<k...@denninger.net> 554- 554-PLEASE READ THIS ENTIRE MESSAGE FOR FURTHER INSTRUCTIONS. . . . = = = = = = = = = Postfix produces a message like this: = = = = = = = = = This is the mail system at host xxx.yyy.zzz. I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to <postmaster> If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system <k...@denninger.net>: host mail.denninger.net[70.169.168.7] said: 554-Subject: SUSPECTED Spam QUARRANTINED - please read for further information 554- 554-The SPAMBLOCK-SYS spam protection system has QUARRANTINED your 554-message to the following user: 554-<k...@denninger.net> 554- 554-PLEASE READ THIS ENTIRE MESSAGE FOR FURTHER INSTRUCTIONS. 554- 554-I employ an application known as "SPAMBLOCK-SYS" to protect my 554-email against . . . = = = = = = = = = (BTW, I think it is BAD for computer programs to send messages humans using "I" to refer to the program. Program's can't be "I" - they are mechanisms, not living things. It's even worse when programs generate text such as "I'm sorry".) Karl assures me his server is putting out newlines for every instance instance of "544-": Postfix is removing the carriage returns. That's broken - Spamblock is emitting CR/LF pairs. I can't see any non-default config items (postconf -n) which would affect this. I am not sure whether the behaviour Karl is expecting is required by an RFC. Is it reasonable to expect the MTA to format the message as qmail does and as Karl expects? Thanks again for Postfix! - Robin
