This article contains information on the default message delivery retry schedule, including the 96-hour or 30-attempt limit, incremental retry intervals, and guidance on modifying these settings with caution.
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 increases incrementally. The longer the message is in the queue, the longer the interval between retries.
The default message delivery schedule is outlined below. These can be amended by Mimecast Support, though there is a minimum number of retries that must be performed, and this should be changed with caution. See the Notifications section below for more details.
| Delivery Attempt | Time Interval | Total Time in Queue |
|---|---|---|
| 1 | Immediate | 0 minutes |
| 2 | 1 minute | 1 minute |
| 3 | 5 minutes | 6 minutes |
| 4 | 9 minutes | 15 minutes |
| 5 | 15 minutes | 30 minutes |
| 6 | 30 minutes | 1 hour |
| 7-15 | 1 hour | 2-10 hours |
| 16-21 | 4 hours | 14-30 hours |
| 22-30 | 8 hours | 38-106 hours |
Delivery Queue Uses
The delivery queue is used to troubleshoot or investigate delayed email delivery. You can also:
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- Force an immediate retry.
- Reject the message for delivery.
- Perform an early (hard) bounce.
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There are several reasons why we may be unable to deliver a message:
| Reason | Description |
|---|---|
| No MX records are available | The DNS lookup cannot be completed. This could be due to the server hosting the MX records experiencing difficulties. |
| No MX records are being returned for the domain | The recipient domain has no valid MX records, or the sender has incorrectly spelled the recipient's domain in the email address. |
| Unable to connect to the remote host | The 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 experiencing a failure. |
| Null result from socket | The system is unable to send data to the socket. |
| Connection timed out | The connection has timed out as the system cannot connect to the remote host. |
| Connection refused | The system is unable to connect to the remote host. |
| Temporary local problem - please try later | The recipient's server is currently unavailable or busy. |
Accessing the Delivery Queue
To access the delivery queue:
- Log in to the Mimecast Administration Console.
- Navigate to Message Center | Message Delivery. The list of messages awaiting delivery is displayed with the following information:
| Column | Description |
| From | Displays the sender's email address. |
| To | Displays the recipient's email address. |
| Email Direction |
An arrow icon displays the direction of the message:
|
| Status / Info |
Displays the status of the message's delivery. The status are:
Other possible statuses are listed in the Message Center: Bounced Messages article. |
| Try | Displays the number of retry attempts (between 1 and 31) for the message. |
| Size | Displays the message's size in KBs. |
| Delivery Status |
Displays a colored icon denoting the message's delivery status:
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- Right-click on a message. A pop-up 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.
| Icon | Action | Result |
|---|---|---|
| Retry Selected Items | Forces a manual retry of the message. | The message delivery is immediately retried, and the retry count increases by one. |
| Reject Selected Items | Rejects the message. | The message is rejected and removed from the delivery queue. A delivery failure notification is sent to the sender of the email. |
| Early Bounce Selected Items | Early bounces the message. | This 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, but the message is recoverable as it has been accepted. |
| Recalculate Delivery Route | Another check is made for a Delivery Routing policy. | When we accept a message for delivery, it is assigned to a Delivery Routing Policy. The original policy can be removed to change the delivery route, and a new policy can be applied. The Recalculate Delivery Route action forces us to review the current policy that applies to the message. |
| Export Data | Exports the message data to a spreadsheet. | Generates a spreadsheet in the selected format with the specified columns. |
Notifications
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.
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 warnings and failure notifications can be amended. See Configuring Notification Sets Definitions and Policies for more information.
The minimum number of retries is:
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- Four retries (15 minutes) for a delivery warning notification.
- Six retries (30 minutes) for a delivery failure notification
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Pausing Inbound Deliveries
If your mail server is down (e.g., for planned maintenance), we will continue to accept inbound emails. 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 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 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 for your entire organization or a specific delivery route.
To pause inbound email delivery to your organization:
- Log in to the Mimecast Administration Console.
- Navigate to Account | Account Settings.
- Select the Pause Inbound Deliveries option.
- Click on the Save and Exit button.
To pause inbound email delivery for a delivery route:
- Log in to the Mimecast Administration Console.
- Navigate to Policies | Gateway Policies.
- Click on the Definitions drop-down.
- Select the Delivery Routing definitions.
- Select the required Definition.
- Select the Pause option.
- Click on the Save and Exit button.
Users can continue using email if they can access a Mimecast end-user application.
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