Recently we implemented so called greylisting on our mail servers. This means that all incoming SMTP sessions with the following new combinations of sending mail server IP address, sender email address and recipient email address gets temporary rejected (SMTP error code 450, meaning: try again later).
From RFC2821: 4yz: Transient Negative Completion reply
The command was not accepted, and the requested action did not occur. However, the error condition is temporary and the action may be requested again. The sender should return to the beginning of the command sequence (if any). It is difficult to assign a meaning to "transient" when two different sites (receiver- and sender-SMTP agents) must agree on the interpretation. Each reply in this category might have a different time value, but the SMTP client is encouraged to try again. A rule of thumb to determine whether a reply fits into the 4yz or the 5yz category (see below) is that replies are 4yz if they can be successful if repeated without any change in command form or in properties of the sender or receiver (that is, the command is repeated identically and the receiver does not put up a new implementation.)
This saves us about 99% of the incoming spam and viruses and is a relief for our mailboxes and the email virusscanners.
Now the bad news, there are some very brain-dead SMTP servers on the internet...
And guess what? They all run on MS Windows. Who had expected that?
Here is the list of them:
MailMax from SmartMax Software Inc.. When receiving an 450, they bounce the mail back to the sender. And this is the error message they are getting:
The 'To' address email@example.com was rejected by the remote server.Which mailserver was it talking to? What was the full error message? What was the error code? And why do you say it's a permanent error while it was a transient error? BRAIN DEAD!
This is permanent error, and the message will not be retried any further.
And they claim on their website:
IMPORTANT: Codes that start with 4 and 5 are the ones that tell you that your message won't be sent until you find and fix the problem.You! Yes you! You should fix the problem, and not the other side, or the MailMax mail server.
Update: With their latest version *version 5.5), at least the error messages are better:
Sorry, your message from <firstname.lastname@example.org> to <email@example.com> could not be delivered. The specific error is: 450 <firstname.lastname@example.org>: Recipient address rejected: BarNet Engineered Transit Delay -- 39 seconds This is permanent error, and the message will not be retried any further.
Still it's a 'permanent' error, but at least it's visible for the person the email was returned to that they interpreted it wrongly.
Sorry, your message from <email@example.com> to <firstname.lastname@example.org> could not be delivered. The specific error is: 450 <email@example.com>: Recipient address rejected: BarNet Engineered Transit Delay -- 45 seconds 2 attempts will be made to re-send your e-mail. Each attempt will be 3 hours apart.
That's much better! Everybody upgrade to the latest version!
CapeSoft Mailer by CapeSoft. It also immediately bounces the email without retrying. BRAINDEAD!
Bigpond.com by Telstra
This is all the attempt of Telstra (Australian ISP) to handle SMTP sessions with a 450 status:
Oct 29 16:17:56 mag postfix/smtpd: NOQUEUE: reject: RCPT from gizmo06ps.bigpond.com[126.96.36.199]: 450 <firstname.lastname@example.org>: Recipient address rejected: BarNet Engineered Transit Delay -- 45 seconds; from=<email@example.com>, to=<firstname.lastname@example.org> proto=SMTP helo=<gizmo06ps.bigpond.com>
That's all: one attempt. And the sender doesn't get an "Your email has failed" message. BRAINDEAD!
InterMail from Openwave Systems Inc..
It doesn't retry at all. (experienced with ozemail.com.au)| Share on Facebook | Share on Twitter