Monitoring the Delivery Queue

Document created by user.oxriBaJeN4 Employee on Sep 11, 2015Last modified by user.oxriBaJeN4 Employee on May 30, 2019
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We attempt to deliver messages to the recipient for up to four days (96 hours) or 30 retry attempts by default, with the Delivery Queue displaying all inbound and outbound messages waiting to be delivered. The time between the retry attempts increase incrementally. The longer the message is in the queue, the longer the interval between retries.


The default message delivery schedule are outlined below. These can be amended by Mimecast Support, though there is a minimum number of retries that must be performed, and should be changed with caution. See the "Notifications" section below for more details.


Delivery Attempt
Time IntervalTotal Time in Queue
1Immediate0 minutes
21 minute1 minute
35 minutes6 minutes
49 minutes15 minutes
515 minutes30 minutes
630 minutes1 hour
7-151 hour2-10 hours
16-214 hours14-30 hours
22-308 hours38-106 hours


Delivery Queue Uses


The delivery queue is used to troubleshoot or investigate delayed email delivery. You can also:

  • Force an immediate retry.
  • Reject the message for delivery.
  • Perform an early (hard) bounce.


There are a number of reasons why we may be unable to deliver a message:


No MX records are availableThe DNS lookup cannot be completed. This could be due to the server hosting the MX records to be experiencing difficulties.
No MX records are being returned for the domainThe recipient domain doesn't have any valid MX records, or the sender has incorrectly spelled the recipient's domain in the email address.
Unable to connect to the remote hostThe remote mail server is temporarily not accepting inbound SMTP connections. This could be due to the recipient mail server subjecting the connection to greylisting, the server being busy, or the mail server could be experiencing a failure.


Accessing the Delivery Queue


To access the delivery queue:

  1. Log on to the Administration Console.
  2. Click on the Administration toolbar menu item.
  3. Select the Monitoring | Delivery menu item. The list of messages awaiting delivery is displayed with the following information:
    FromDisplays the sender's email address.
    ToDisplays the recipient's email address.
    Email DirectionAn arrow icon displays the direction of the message:
    • Inbound_Email.gif: Inbound
    • Outbound_Email.gif: Outbound
    Status / InfoDisplays the status of the message's delivery:
    Queued for delivery Info: (none).We're attempting to connect and deliver the message.
    Bounce - Recipient Domain has no MX Records Info: Domain has no MX records or is invalid.The DNS lookup is producing empty MX records, typically due to a spelling mistake in the email address's domain.
    Unable to retrieve MX records from DNS Info: Temporary error looking up MX record.The DNS lookup cannot be completed, possibly due to DNS server issues.
    Unable to connect to remote host Info: Connection refused or connection timed out.The destination mail server rejected the connection or cannot be reached.
    Could not progress past recipient in protocol Info: Value displayed was the temporary error code that the remote mail server passed back to our platform.The destination mail server responded with a temporary error.
    Recipient server unavailable Info: 451.The destination server could not be contacted, although the IP address was resolved.
    Inbound email delivery suspended Info: (none).Inbound deliveries have been paused for the account.

    Other possible statuses are listed in the Bounce Viewer page.

    TryDisplays the number of retry attempts (between 1 and 31) for the message.
    SizeDisplays the message's size in KBs.
    Delivery StatusDisplays a colored icon denoting the message's delivery status:
    • Red: The message is locked for delivery.
    • Orange: The message is queued for delivery.
    • Green: The message is waiting for the next retry interval.
  4. Right click on a Message. A popup menu is displayed that allows you to perform one of the following actions:
    These actions can be performed on multiple messages by selecting the check box next to the messages and selecting a toolbar option.
    Retry Selected ItemsForces a manual retry of the message.The message delivery is immediately retried, and the retry count increases by one.
    Reject Selected ItemsRejects the message.The message is rejected and removed from delivery queue. A delivery failure notification is sent to the sender of the email.
    Early Bounce Selected ItemsEarly bounces the message.Causes the delivery attempts to be increased to a maximum of 30 attempts, causing delivery to fail. A delivery failure notification is sent to the sender of the message, but the message is recoverable as it has been accepted.
    Recalculate Delivery RouteAnother check is made for a Delivery Routing policy.When a message is accepted by us for delivery, it is assigned to a Delivery Routing Policy. To change the delivery route, the original policy can be removed and a new policy applied. The Recalculate Delivery Route action forces us to review the current policy that applies to the message.
    Export DataExports the message data to a spreadsheet.Generates a spreadsheet in the selected format with the specified columns.




A delivery warning notification is sent to the sender after the warning period (six attempts or one hour by default) notifying them of a delay in delivery.

Delivery Warning

Once a message's delivery has timed out (30 attempts or 96 hours by default) a delivery warning notification is sent to the sender, and the failure is logged in the Bounced Messages as a hard bounce.

Delivery Failure

Delivery warning and failure notifications can be amended. See Configuring Notification Sets Definitions and Policies for more information.

The minimum number of retries is:

  • Four retries (15 minutes) for a delivery warning notification.
  • Six retries (30 minutes) for a delivery failure notification


Pausing Inbound Deliveries


If your mail server is down, for example for planned maintenance, we will continue to accept inbound email. Messages are held in the delivery queue, and we will attempt to deliver to the mail server based on the delivery schedule described above. Once your mail server is back online, you can wait for the message to be delivered according to the schedule, or you can manually retry messages in your delivery queue. We will attempt to deliver a message for up to 30 attempts over a period of 6320 minutes (four days). If the outage is longer than this, we will issue a Non Delivery Report (NDR) to the sender.


If you're experiencing an issue that is resulting in (some of) your inbound messages getting rejected or bounced by your mail server, you can temporarily pause inbound mail delivery. You can do this either for your entire organization, or for a specific delivery route.


To pause inbound email delivery to your organization:

  1. Log on to the Administration Console.
  2. Click on the Administration toolbar menu item.
  3. Select the Account | Account Settings menu item.
  4. Select the Pause Inbound Deliveries option.
  5. Click on the Save and Exit button.


To pause inbound email delivery for a delivery route:

  1. Log on to the Administration Console.
  2. Click on the Administration toolbar menu item.
  3. Select the Gateway | Policies menu item.
  4. Click on the Definitions drop down.
  5. Select the Delivery Routing definitions.
  6. Select the required Definition.
  7. Select the Pause option.
  8. Click on the Save and Exit button.


Users will be able to continue using email if they've access to a Mimecast end user application.


See Also...


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