Part II, Troubleshooting MTA Message Queues

As I mentioned previously, the topic of message build-up in the MTA message queues prompted this writeup. Here's the second part of this installment, providing some details on what you can do if you discover that your deployment is having an actual problem with message build-up.

Before You Begin

At a minimum, you need to enable logging for the channels that you want to troubleshoot. The amount of logging that you set (log level) depends on your situation. To enable logging on a channel and learn about other options, see Managing MTA Message and Connection Logs in Sun Java System Messaging Server 6.3 Administration Guide for more information.

Troubleshooting TCP Channels

This section describes a general approach to troubleshoot build up of messages in TCP message queues to determine if there is an actual problem.

  1. When you suspect that there is something happening that is more than the store-and-forward aspect of messages building up in a message queue, begin by using the imsimta qm summarize command.

    For more information, see imsimta qm in Sun Java System Messaging Server 6.3 Administration Reference.

  2. The imsimta qm summarize command can greatly impact your system if you have a large backlog of messages. Instead of running this command frequently, consider using the imsimta qm messages channel command instead.

    This command lists the destination hosts for which messages are queued in the specified channel. This command also lists how many messages are waiting for their next schedule retry (the delayed messages column) versus how many are ready to be retried now (active now). When you use the imsimta qm messages command, you must specify a channel name; a wildcard is not valid input. For example:

    # imsimta qm
    qm.maint> messsages tcp_local
    host                             active messages  delayed messages
                              0                 2000
                                0                 3000

    In this example, 2,000 messages are waiting for their next scheduled retry to be delivered to, and 3,000 are waiting for their next scheduled retry for delivery to

    Note - The Messaging Server 6.3 release removed the imsimta qm messages command. However, Messaging Server 6.3 does contain a new, useful command—imsimta qm jobs—to help understand why messages are not being delivered.

    This information is also useful for the situation where messages have failed and are waiting to be retried. If you see there are many messages in a channel queue, but most of them are delayed, this probably indicates the problem is with the remote domain. See Destination Host Problems for information on how to workaround this problem.

    Note - A message can be in process of being tried by a job, or on a channel waiting to be tried, or on a channel waiting to be retried. The messages command active messages column includes messages which have not been tried yet and those which were previously delayed and are now ready to be tried again. That is why you might see a zero (0) in this column. In Messaging Server 6.3, you can see the messages being retried with the new jobs command.

    iPlanet Messaging Server 5. Use top -to channel or top -domain_to channel to analyze what is going on in that channel.

  3. Look for trends on your system. For example, when most of the mail is all destined for one remote domain, check the status of that remote domain.

    Additionally, look in the mail.log_current file to determine what has happened in recent history when you tried to send mail to that remote domain.

  4. Use the imsimta qm dir -to address command to select a group of messages. Then use this information to look at the delivery attempt history of some of the messages. (You use the sequence numbers from the dir listing). Often, you will find that these messages are all non-delivery notifications for spam, which was not deliverable. If this is the case, determine how those original spam messages got into the system in the first place. Verify that the messages are spam by using the imsimta qm subcommands dir, read, and history. If this is indeed the case, think about routing the non-delivery notifications through a different outbound channel, thereby preventing them from choking the normal tcp_local channel queue.

    For example, use the notificationchannel and dispositionchannel keywords to specify an alternate process channel to queue delivery status notifications and modify status notifications, respectively. Then you use source-specific rewrite rules to direct messages from these process channels to a particular tcp_\* channel set to only use a few processes/threads. For more information, see Source-Channel-Specific Rewrite Rules ($M, $N) in Sun Java System Messaging Server 6.3 Administration Guide.

  5. Verify that the master process for the channel is started. The tcp_\* channels all use the smtp_client process. To find out which process is associated with which channel, in respect to dequeuing, see the master_command parameter in the associated channel block in the job_controller.cnf file.

Destination Host Problems

When you have determined that messages are queued to an unavailable remote host, you have two options:

  1. Create a new channel for the host. If this host is consistently a problem, all future email will go to this new channel. For existing messages that are enqueued, you can either wait for the problem with the destination host to be resolved or delete the messages from the queue.

  2. Increase the number of delivery threads for the channel, or set a ceiling on the number of queued messages that will trigger a new thread or process to start. See the max_client_threads parameter in the channel option file and the threaddepth channel keyword, respectively.

Troubleshooting the ims-ms Channel

This section describes a general approach to troubleshoot build up of messages in the ims-ms channel. The four general cases where the ims-ms channel shows a build-up of messages in the queue are:

  • IMAP_MAILBOX_LOCKED. While you might see this error in a message file that is briefly in the queue area, typically such a message file doesn't remain for long. The error only repeats in a message file in the queue area if the mailbox is remaining locked for an extended period. The job controller retries delivery of these messages after short delays until either the message gets delivered or a different error is encountered.

  • IMAP_MAILBOX_BADFORMAT, IMAP_MAILBOX_NOTSUPPORTED. The mailbox is most likely corrupted. This case rarely occurs. You might want to use the reconstruct command for these cases.

  • IMAP_IOERROR. The message store is most likely corrupted or otherwise inaccessible. This case occurs even more rarely.

  • IMAP_QUOTA_EXCEEDED. The user or users are over quota. This is the most common case, which this technical note discusses below.

Note - If the channel gets a permanent delivery failure error, then the message is immediately bounced and does not remain in the ims-ms queue area.

To troubleshoot the ims-ms channel, use the following high-level approach:

  1. Perform a similar investigation as you would for tcp_\* channels by using the imsimta qm summarize command to view what is happening on the system.

  2. Use the imsimta qm history command to examine the message IDs to detect if there are different sorts of messages. For example, you might see:

    Message id: 800
    Filename: /opt/SUNWmsgsr/data/queue/tcp_local/001/ZZf0b0KaNZykG.00

    A message's file name starting with ZZ indicates that it has not been tried yet. The message file name is a counter starting at ZZ and decremented (ZY, ZX, and so on) each time the message is tried, fails, and is reenqueued for later retry. Thus, a ZZ\* file name has not been tried yet, and there is no history.

    In general, but not always, when you have non-ZZ\*, non-.HELD files in the queue area, you have the IMAP_QUOTA_EXCEEDED case. (The frequency with which you see IMAP_MAILBOX_LOCKED conditions probably depends upon user and email client characteristics. This condition is more common with users who like to receive and move around lots of large attachments but it should typically occur rarely.)

    For a site that enforces quota, probably most of the non-ZZ\*, non-.HELD messages in the ims-ms queue area are there because of the recipient user being over quota. Verify this is the case by running the imsimta qm command with the history subcommand. You should see “over quota" in the history of the over-quota messages.

    Note - In iPlanet Messaging Server 5.2, the imsimta qm top command was enhanced to have more sorting options.

  3. Are there any Q status messages in the mail.log_current file pertaining to the ims-ms channel? When you see “mailbox is busy” and Q status in the mail.log_current file, then the message is put back on the queue to be retried later as per the job controller's scheduling and the backoff keyword on the channel.

  4. If not, check that the ims_master process is running. Are there any errors in its log file (the imta file)? The ims_master process could be hung. Use the imsimta process command to verify running processes.

Use the following strategies for users who become over quota:

  1. Inform users of the need to perform mailbox maintenance to return to under quota status, or increase their quota.

  2. Reduce the time that mail is queued for over quota accounts before being bounced back as over quota. See the store.quotagraceperiod configutil parameter. If you don't want to queue email for over quota accounts (and bounce the message straight back), set this parameter to 0 (that is, no grace period). This parameter is available in iPlanet Messaging Server 5 as well.

  3. For Messaging Server 6, you can enable the configutil parameter. This enables quota enforcement before messages are enqueued in the MTA and prevents the MTA from filling up.

More About the ims-master Process

At times you might see the ims-master process shutting down and starting up in the log file:

# > imta /opt/SUNWmsgsr/logs
# grep "Sun Java" imta
[30/Aug/2006:17:05:05 -0400] learn ims_master[19736]: General Notice: Sun Java(t
m) System Messaging Server ims_master 6.2-7.02 (built Jun 13 2006) shutting down
[30/Aug/2006:17:05:20 -0400] learn ims_master[28310]: General Notice: Sun Java(t
m) System Messaging Server ims_master 6.2-7.02 (built Jun 13 2006) starting up
[30/Aug/2006:17:07:24 -0400] learn ims_master[28310]: General Notice: Sun Java(t
m) System Messaging Server ims_master 6.2-7.02 (built Jun 13 2006) shutting down
[30/Aug/2006:17:07:32 -0400] learn ims_master[28380]: General Notice: Sun Java(t
m) System Messaging Server ims_master 6.2-7.02 (built Jun 13 2006) starting up
[30/Aug/2006:17:19:31 -0400] learn ims_master[28380]: General Notice: Sun Java(t
m) System Messaging Server ims_master 6.2-7.02 (built Jun 13 2006) shutting down

This is normal operation and does note indicate a problem. This is a “notice” message (not an “error” or “critical” level message). As with all channel jobs, ims-ms channel jobs shut down from time to time based on either having nothing to do, or based on “timing out” (getting old). Then the job controller restarts new jobs as needed.

Configuration Issues

You might want to increase the number of processes the job controller can start for the tcp_local, tcp_intranet, or other tcp_\* channels, or increase the number of threads each of those processes will start. You might also want to give the tcp_local channel its own pool. If you observe queued messages (total across all queues) to be greater than 100,000, increase the value of MAX_MESSAGES for the job_controller.cnf setting. See Job Controller Configuration File in Sun Java System Messaging Server 6.3 Administration Reference for more information.

Additional Information

This section contains additional information to help you understand MTA operations.

What Are .HELD Messages?

If the MTA detects that messages are bouncing between servers or channels, delivery is halted and the messages are stored in a file with the suffix .HELD in the msg-srv-base/data/queue/channel directory. Typically, a message loop occurs because each server or channel thinks the other is responsible for delivery of the message. You need to manually fix these .HELD messages with the imsimta process held command.

There is an unfortunate collision of terminology and concepts between .held messages and the hold channel. And worse still, the command to process .held messages is called release, whereas the command to process messages on the hold channel is called process_held.

You use the hold channel to hold messages of a recipient temporarily prevented from receiving new messages. For example, you might be moving a user's mailbox and want to hold new incoming messages. The hold channel is located in the msg-svr-base/queue/hold directory. Messages are written to this queue as ZZxxx.held files. Because the job controller doesn't “see” these .held files, they are not dequeued for delivery. You release these files with the imsimta qm release command, and the reprocess daemon reprocesses them.

See To Temporarily Hold Messages Using the Hold Channel in Sun Java System Messaging Server 6.3 Administration Guide for more information.

How Does a Message Become a .HELD Message?

Messaging Server makes use of MAX_\*_RECEIVED_LINES options that you set in theoption.dat file to determine when a message is put into the .HELD state. The most relevant options and their default values are:




Once a message has looped through the MTA enough to accumulate MAX_RECEIVED_LINES header lines indicating the local MTA, then the message becomes .HELD. You can cause the MTA to immediately recognize that it has connected to itself, rather than waiting to accumulate MAX_LOCAL_RECEIVED_LINES local Received: headers, by specifying the loopcheck keyword on the appropriate channel(s) in the imta.cnf file.

For More Information on Troubleshooting the MTA

Use the following to aid in troubleshooting the MTA:


Great Post!!

By the way i have a problem with only one mailbox (fortunately is mine) i can't dequeue the messages going to it, here are some mail.log_current lines that ilustrates this behaviour:

8-Jun-2007 13:05:30.06 ims-ms Q 25 rfc822; ichaveronospam@ims-ms-daemon Mailbox is busy Mailbox is busy

28-Jun-2007 13:05:30.11 ims-ms Q 12 rfc822; ichaveronospam@ims-ms-daemon Mailbox is busy Mailbox is busy

28-Jun-2007 13:05:30.11 ims-ms Q 6 rfc822; ichaveronospam@ims-ms-daemon Mailbox is busy Mailbox is busy

This account haves no quota assinged, i'm kind o stuck on this one. I hope you can take the time to give some advice. Thanks!!

Posted by Ivan Chavero on June 28, 2007 at 06:15 AM MDT #

Ivan: I checked w/ one of our experts. Here's the response I got:

"Mailbox is busy" can mean just that, another email was being delivered at the same time or the mailbox was locked from changes because another action was being performed (imap expunge or alike). The way around this is to have faster I/O infrastructure which will allow emails to be delivered quicker, mailbox modifications to happen faster etc. which will free up the locks sooner. There could also be more serious issues, such as an orphan lock on the account, but this would be a continuous problem (all emails not delivered).

So if the account is a busy one (lot's of new emails/lots of accesses & changes) and there are "Q" every so often, no big deal. The emails will be reattempted for delivery at a later date and delivered.

If _all_ emails are getting this message for a specific account(s) (so no new emails are being delivered) then there could be an orphan lock (which is usually caused by a crashed process). Clearing this lock involves restarting messaging server -- but if a process did crash this needs to be investigated further (enabling coreadm, provided core file to Sun support for review, that sort of thing).

Posted by Joe Sciallo on June 29, 2007 at 02:09 AM MDT #

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