The Delivery Queue

Document created by user.oxriBaJeN4 Employee on Sep 11, 2015Last modified by user.oxriBaJeN4 Employee on Mar 25, 2018
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The Delivery Queue displays all messages (inbound and outbound) waiting to be delivered by us. We attempt by default 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 a 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 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, which 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 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. Select the Administration toolbar menu item.
  3. Select 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).We are 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, possibly 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 our 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, you can perform one of the actions below by right clicking a message. For multiple entries, use the check box next to the message, and select from the options in the 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 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 button forces us 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 follow our delivery retry schedule. The time between the retry attempts increase incrementally. The longer the message is in the queue, the longer the interval between retries. 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


Notification Examples


Warning notifications are sent after six failed attempts (one hour). Messages "hard bounce" after 30 attempts (four days after the message was initially sent). The delivery warning and failure notifications can be amended. 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.
  • 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, 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 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. 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 email 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.


To pause inbound mail delivery for your entire organization:

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


To pause inbound mail delivery for a specific delivery route:

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


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

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