"Connection to the destination SMTP was closed" errors

[ehavemann]

Frequently, we get the following warning after sending an email:

"Mail System Error - Undeliverable Mail (Warning Only)
This is only a warning, please do not resend!
The following mail has not yet been delivered and has been in our queue for 30 minutes. We will
continue trying to deliver the mail for a total of 9600 minutes before it is failed.

From: xxxx
Sent: Sun, 16 Aug 2009 21:52:25 -0400
Subject: xxx
To:-
xxx at xxx - Connection to the destination SMTP was closed."

Most of the time the email will eventually go out. But what in general does this error mean, and what could cause this error? AMS is running on a dedicated Windows XP box, but it isn't the fastest thing out there. DNS performance is fair, not great, as measured by a utility program running on the XP box that performs DNS lookups.

[Code Crafters]

The error indicates that the remote mail server has closed the connection without giving a reason for why it is closing. Usually this is due to SPAM / security filtering reasons so the destination mail server doesn't want to tell you why it's refused the connection. If the mails are eventually delivered, it could be similar to grey listing by seeing if you'll retry when refused the first time. However, the mail server should give an appropriate 421 temp failure error if this is the case but of course this is its decision. You can contact the destination mail server for more details on what caused the connection to be closed. You can also check the outmail logs to see if any other errors were given when mail sending fails.

Any machine at least 1GHz (ideally 2GHz) CPU with 128MB RAM or more will run AMS fine. If you have a very busy mail server then of course a good system will help with the speed of processing but it will run stable on a very basic machine. For DNS, ideally you should use your ISPs DNS servers rather than a local DNS server for better DNS resolution and better mail delivery.