The Delivery Queue

Document created by user.oxriBaJeN4 Employee on Sep 11, 2015Last modified by user.oxriBaJeN4 Employee on Jun 15, 2017
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The Delivery Queue displays all messages (inbound and outbound) waiting to be delivered by Mimecast. Mimecast will by default attempt to deliver messages to the recipient for up to four days (96 hours) or 30 retry attempts, as described below. A delivery warning notification is sent to the internal sender after the warning period (by default six attempts or one hour) notifying them of the delay in delivery. Once a message's delivery has timed out (a default of 30 attempts or 96 hours), a delivery warning notification is sent to the sender, and the failure is logged in the Bounced Messages as a hard bounce. These retry schedules can be amended by Mimecast Support if required, but should be changed with caution.


The Delivery Queue is generally used by Administrators to troubleshoot or investigate delayed email delivery. They can also:

  • Force an immediate retry
  • Reject the message for delivery
  • Perform an Early Bounce (Hard Bounce)


There are a number of reasons why Mimecast may be unable to deliver a message. These include:


No MX records are availableThe DNS lookup cannot be completed, which could be due to the server hosting the MX records to be experiencing difficulties.
No MX records are being returned for the domainEither the domain of the recipient does not have any valid MX records, or the sender has incorrectly spelled the recipient's domain name in the email address.
Unable to connect to 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.


To access the Delivery Queue

  1. Log in to the Administration Console.
  2. Click on the Administration toolbar button. A menu drop down is displayed.
  3. Click on the Monitoring | Delivery menu item.


FromEmail address of sender.Details of the sender.
ToEmail address of recipient.Details of the recipient.
Email Direction

Arrow indicator Inbound Arrow Indicator Outbound.


Show the direction of the message (inbound or outbound).

Status and Info

(For other possible statuses, view the Bounce Viewer article)

Status: Queued for delivery Info:  (none).Mimecast is attempting to connect and deliver the message.
Status: 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.
Status: Unable to retrieve MX records from DNS Info: Temporary error looking up MX record.The DNS lookup cannot be completed, possible due to DNS server issues.
Status: Unable to connect to remote host Info: Connection refused or connection timed out.The destination mail server rejected the connection or cannot be reached.
Status: Could not progress past recipient in protocol Info: Value displayed was the temporary error code that the remote mail server passed back to the Mimecast platform.The destination mail server responded with a temporary error.
Status: Recipient server unavailable Info: 451.The destination server could not be contacted, although the IP address was resolved.
Status: Inbound email delivery suspended Info: (none).Inbound deliveries have been paused for the account.
TryNumeric value between 1 and 31.The number of retry attempts for this message.
SizeNumeric value in Kilobytes.Size of the message.
StatusLocked (Red Indicator)The message is currently locked for delivery.
Delayed (Orange Indicator)The message is queued for delivery.
Normal (Green Indicator)The message is awaiting the next retry interval.


Once the message has been located, administrators are able to manually Retry, Reject or Early bounce a message in the Delivery Queue. To do so, right click on the message (or click on the context menu icon and select the desired action). For multiple entries, use the check box next to the message, and select from the options in the top toolbar:


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 internal 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 internal sender of the message, but the message is recoverable as it has been accepted.

Recalculate Delivery RouteMimecast rechecks for an active Delivery Routing policy.

When a message is accepted by Mimecast for delivery, it is assigned to a specific Delivery Route Definition through a Delivery Routing Policy. To change the Delivery Route for that message, the original policy can be removed, and a new policy applied. The Recalculate button forces Mimecast to review the current policy that would apply to the email awaiting delivery.    

Export DataExports the list items to a spreadsheet.Generates a spreadsheet in the selected format with the specified columns


Retry Attempts


All messages in the Delivery Queue will follow the Mimecast delivery retry schedule. The time between the retry attempts will increase incrementally, the longer the message has been in the queue, the longer the interval between retries will be. The email delivery schedule is configured by default as follows:


Delivery Attempt
Time IntervalTotal Time in Queue
1Immediate0 minutes
21 minute1 minute
35 minutes6 minutes
49 minutes15 minutes
515 minutes

30 minutes

630 minutes1 hour
7-151 hour2-10 hours
16-214 hours14-30 hours
22-308 hours38-106 hours


Warning notifications are sent out after 6 failed attempts (1 hour).  Messages will "hardbounce" after 30 attempts (four days after the email was initially sent).

The Delivery Warning and Failure user notifications can be amended by the Administrator. See Configuring Notification Sets Definitions and Policies for more information.
Delivery Warning Notification Example


Delivery Failure Notification Example


  • The default delivery attempts for warning and failed message notifications can only be amended by Mimecast Support, and should be changed with caution. Contact Mimecast Support to discuss this option.
  • The minimum number of retries for the Delivery Warning Notification is four retries (15 minutes after the email was sent). The minimum number of retries for the Delivery Failure Notification is six retries (30 minutes after the email was sent).


Pausing Inbound Deliveries


If your mail server is down for planned or unplanned reasons, Mimecast will continue to accept inbound email. The message will be held in the Delivery Queue and Mimecast will attempt to deliver to the mail server based on the email delivery schedule as 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 the messages held in your Delivery Queue.


Mimecast 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, Mimecast will issue a Non Delivery Report (NDR) to the email sender.


If you are experiencing an issue that is resulting in (some of) your inbound messages getting rejected or bounced by your mail server, it is possible to temporarily pause inbound mail delivery. This can be done in two ways:


  1. For your entire organization:
    1. Click the Administration | Account | Account Settings menu item.
    2. Click the Pause Inbound Deliveries option.
    3. Click the Save and Exit button.
  2. For specific mail Delivery Routes:
    1. Click the Administration | Gateway | Policies menu item.
    2. Click the Definitions drop down.
    3. Select the Delivery Routing menu item.
    4. Select the required Definition.
    5. Select the Pause option.
    6. Click the Save and Exit button.


Users will be able to continue using email if they have access to either Mimecast Personal Portal,  Mimecast for Outlook, or Mimecast Mobile applications.

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