What are the SMTP errors that can appear in the mail logs?
SMTP error messages fit into two broad categories. They are:
- Deferred - A temporary failure where SMTP could not handle the transaction, but the system tries again later.
- Rejected - A permanent failure where SMTP could not handle the transaction at this time, and is never able to handle it, so it is rejected out of hand.
Both can refer to a message as a whole, or to a single recipient of a message. When the error message refers to a message, the whole message was deferred or rejected. When the error message refers to a specific user or hostname, the message to that user or host was deferred or rejected while other recipients of the same message may still receive the message.
If an error message contains a queue ID (QID) prefix, the sender has been sent a notification email with status of their message. A QID is assigned to the bounced message that is the notification email the sender receives. The administrator can use this identifier to find the message in the system logs.
The following is a list of possible SMTP error messages, their meaning, and the way they appear in the mail logs:
- 4xx UserAddress Reason - Mail to the specified address was not delivered for the specified reason, but the system tries again later.
00:13:43 Deferred: 453 email@example.com... User fred mailbox full
- 5xx UserAddress Reason - The message sent to the specified address was rejected for the specified reason.
14:04:27 rejected 550 <firstname.lastname@example.org>... Relaying denied
- Bounced message - The message was not delivered for some other error than those specified below.
08:42:13 bounced message: 450 Internal error
- Cannot send message within X days - The message has been deferred for the specified number of days, and the system does not try again.
11:10:17 AEH41708: Cannot send message within 5 days
Where AEH41708 is the QID of the notification message the sender receives.
- Connection refused by Hostname UserAddress - The system is up, but SMTP is not responding. Something between the Mirapoint appliance and the specified host actively rejected our attempt to talk to them. The system tries again later.
16:26:11 Deferred: Connection refused by x.y.com. email@example.com
- Connection reset by Hostname - The connection to the specified host name was reset by the remote system (they hung up).
00:13:53 Deferred: Connection reset by mailbox.example.com
- Data format error - Usually this means someone is trying to send 8-bit data to a remote server that doesn't understand it, but it can also mean that the remote server might have committed a protocol violation. This could also refer to a specific user, where the data error occurred when trying to send to the specified user "to address." The Mirapoint system has given up trying to deliver it.
02:34:21 AEH39487: Data format error
02:34:21 Data format error firstname.lastname@example.org
- Deferred UserAddress - Mail sent to the specified address was not delivered, but the system retries again later.
02:40:53 Deferred email@example.com
- Host unknown - The specified host is not known. Either the message "to address" was incorrectly typed, or there could be a DNS problem.
03:59:28 AEH39758: Host unknown
- Host unknown UserAddress - The specified system hostname has not been found in DNS.
16:27:00 Host unknown firstname.lastname@example.org
This includes an address and is what we could not look up or find in the DNS.
- Message Filtering dropped message: 250 Silently rejected - A domain filter was written that was instructed to drop the message.
23:24:46 Message Filtering dropped message: 250 Silently rejected
- No route to host Hostname - The Mirapoint cannot figure out how to get network packets to the specified host, which could indicate your network is misconfigured.
11:51:32 Deferred: No route to host ams1.example.com
- Null connection from Hostname IPaddress - A connection from the specified host was made, then disconnected without issuing any SMTP commands.
00:00:27 Null connection from crockett.example.com [192.168.1.7]
You may not see a hostname in this error message; if DNS fails, you see only the IP address.
- Operation timed out with Hostname - A network operation could not be completed and mail to the specified hostname was not delivered, but the system tries again later. The specified host could be down, or there is a break in the network.
00:00:55 Deferred: Operation timed out with cutb.example.com
- Return receipt - The sender requested notification that their message was delivered, and we are notifying them by return mail.
11:33:03 AEH41895: Return receipt
- Service unavailable - The message needs a resource the system cannot provide (for example, the message exceeds the Maxmsg size, has too many recipients, etc.), and the message could not be delivered.
13:02:13 AEI00403: Service unavailable
- Split from QID - The message filtering caused the message just sent to have a new queue ID assigned to it.
- Timeout waiting for input from Hostname - The specified remote host was communicating with the Mirapoint system, but then "hung" or stopped communicating. After waiting for a period of time, the Mirapoint gives up.
07:32:23 rejected timeout waiting for input from mfs-pci.example.net
- Unexpected close on connection from Hostname - The specified remote host abruptly terminated the connection while the Mirapoint was sending the message (the equivalent of hanging up on caller mid-sentence). The specified remote host may have crashed, their SMTP stopped, or some other failure occurred.
01:01:33 rejected unexpected close on connection from ci37.example.com,
sender=<"Fred Smith"<email@example.com>>: Undefined error: 250
- User unknown - There is no such user at the specified host.
00:51:03 AEH38945: User unknown
- Warning: could not send message for past X hours - The message has been deferred for the specified number of hours, and is still deferred.
03:47:44 AEH39723: Warning: could not send message for past 4 hours
If the originator is `Not Available,' the sending SMTP client hung up prior to issuing the Mail From command.
If the originator is set, but QID is `No QID,' the sending SMTP client hung up prior to issuing the Data command.
If originator and QID are set, but bytes is set at zero, then a null message was sent, or the sending SMTP client hung up after sending the Data command.