Deliver Pre-Flight Checks

Before sending a Deliver message, review the Pre-Flight Checks. These errors and warnings identify common mistakes, but they should not be used exclusively for message review. Always test and review all aspects of a Deliver message, including recipient lists, the message itself, and intended settings prior to activation.

Please note that Pre-Flight Checks only display for Version 1 of a split test mailing.


Pre-Flight Check errors appear in red and will prevent activation of a mailing. Errors will appear under the following circumstances:

Message Corrective Action(s)
"Error: Recipient field is missing" Enter a value—using a merge field (e.g., {{email}}) or a static email address—in the Recipient field
"Error: Mailing does not contain any recipient lists" Add at least one recipient list to the mailing
"Error: One or more recipient lists use an identity-aware population that was created outside of Deliver. Edit and re-save any existing recipient lists in Deliver to bypass this message"

Add a user to the recipient list using an identity-aware population by:

  1. Visiting the recipient list
  2. Clicking "Edit"
  3. Specifying a user
"Error: Message cannot be activated while archived"

Unarchive the message by:

  1. Clicking "Edit"
  2. Clicking "Unarchive"
"Error: Stop date/time has already passed. Message will not send unless stop date/time is blank or occurs in the future"

The Stop Date/Time is set either (i) automatically when a mailing is deactivated or (ii) manually. Unset the value by:

  1. Clicking "Edit"
  2. Clicking "Continue running mailing indefinitely"
  3. Clearing the Stop Date/Time value
"Error: For compatibility with all recipient mail servers, attachments cannot exceed 2MB in the aggregate. (Current Total = (#) MB)"

Use either (i) a smaller attachment or (ii) link to the attachment. For the second option, the attachment can be added to Slate using the File Editor tool

"Error: SMS requires an active sender number"

Activate the mailing by:

  1. Purchasing credits, if applicable
  2. Add an account that uses the "SMS/Voice" Service


"Error: There is a negative balance of message credits. Add at least (#) additional credits to restore a positive balance"

Purchase additional credits in the Deliver Configuration tool

"Error: SMS is not available in a test environment"

SMS messages can only be activated in production environments

"Error: Message contains one or more links using merge fields without the <other> protocol designation"

This error appears when (i) a merge field is the first component of a URL and (ii) the Protocol is either "http://" or "https://".

Adjust the Protocol by:

  1. Editing the URL
  2. Changing the protocol to "<other>"
"Error: Message contains one or more tracking links from another message"

To track URL clicks, Slate rewrites each URL. These tracking URLs contain the domain "mx.technolutions". When a link is copied from a message sent from Slate, the link will contain that unique tracking URL.

Resolve this error by:

  1. Opening the mailing's source
  2. Search for any URLs that contain "mx.technolutions"
  3. Replace those URLs with their direct URL (e.g.,
"Error: Message body appears to have been corrupted by Grammarly. Uninstall the Grammarly extension, clear the HTML contents of the message, and then re-type your message to remove all corruption by Grammarly"

The Grammarly extension is known to cause serious corruption to messages created or updated using web-based HTML editors. The resulting HTML is likely to be clipped or blocked by email service providers, including Gmail.

Resolve this error by:

  1. Uninstalling the Grammarly extension
  2. Using the Source button in the HTML editor to clear the contents of the message
  3. Retyping the message
"Error: Message body contains <script> tags, which may result in the message being blocked"

Resolve this error by:

  1. Opening the mailing's source
  2. Remove <script> tags and their contents

Note: Some browser extensions may inject unintended <script> tags in the message source. If <script> tags persist, deactivate browser extensions prior to editing the mailing's source. Once the message is saved, confirm that no <script> tags have been re-added.

"Error: Message body is larger than 256KB, which may result in the message being blocked"

Email providers often block messages that exceed 256KB.

Reduce the message's size by:

  • Removing/replacing large images
  • Reduce excessive text (e.g., using Liquid markup or Mailing Content Snippets)
"Error: Message body contains redirector links from another email client"

One or more links in the message body were copied from an email message in Microsoft Outlook Web Access (OWA). These links will not load correctly for external users. The links will contain /owa/redir. For more information, visit this Microsoft Support Page.

Resolve this error by removing the redirector link(s).


Pre-Flight Check warnings appear in orange and will still allow users to activate the mailing, though it is recommended to resolve these identified issues prior to activation. If a user attempts to activate a mailing while a warning is present, the user will be prompted to type a confirmation message. Warnings will appear under the following circumstances:

Message Corrective Action(s)
"Warning: Recipient field does not contain a merge field" The recipient field in the message contains a static email address or addresses, rather than a merge field. If the intent is to send messages specifically to one email address, then this warning can be ignored. If the message must be sent to each email address within a recipient list, then the Recipient should be updated to use a merge field (e.g., {{email}})
"Warning: Custom SQL queries are strongly discouraged for recipient lists and may prevent some pre-flight checks from being evaluated" It is not recommended to use Custom SQL queries as recipient lists. In most cases, Custom SQL queries are not necessary for Deliver mailings, so they should be migrated to use a query base within the Query Builder tool.
"Warning: It appears that you might be sending a decision-related email. Check your message, recipient lists, and estimated recipient counts to ensure that you are sending the right message to the right population"

It is never recommended to send an email with decision information. Instead, decision letters should be assigned to the application to be viewed on the status page when a decision is released via the Release Decisions page. There is a Decision Notification System mailing that can be configured to alert applicants of a released decision without telling the applicants what the decision is. This process helps to prevent accidentally offering admission to applicants who do not have an admit decision.

If the message contains any of the following decision-related terms, this warning will appear:

  • admitted
  • acceptance
  • congratulations
  • deposit
  • enroll
  • deny
  • regret
  • waitlist
  • wait list

This warning should only be ignored if the message is unrelated to decisions, and the message just happens to use these words.

"Warning: Bulk SMS messages are recommended to contain a merge field, such as the recipient's name, to avoid being blocked by mobile carriers"

Mobile carriers block messages that are perceived to be spam. One best practice to ensure deliverability of SMS messages is to include a merge field, such as the person's first name. This personalization is often enough to prevent mobile carriers from blocking the message

"Warning: MMS picture messages are not currently recommended for bulk communications, as they are more likely to be blocked by mobile carriers than text-only messages"

Mobile carriers block messages that are perceived to be spam. MMS picture messages are more likely to be blocked than text-only (SMS) messages. Therefore, SMS messages are recommended to improve deliverability

"Warning: One or more recipient lists have existing query executions that were manually run. These records will not be considered unless the executions are removed prior to activation"

If a query run is manually executed prior to the mailing being sent, this warning will be displayed. If the records present in that query run should be included when the mailing is sent, remove the run by taking the following steps:

  1. Open the recipient list
  2. Click on the query run
  3. Click "Edit Properties"
  4. Click "Delete Run"
"Warning: {{merge field}} in reply/sender/recipient/cc/subject/body missing in . . ."

This message will appear when a merge field within the message is not defined within one or more recipient lists. The warning message lists the name of the merge field, the location where it is used, and the recipient list that does not include that merge field. Use this information to help you find the erroneous merge field.

All available merge fields appear on the right side of the Edit Message window. Confirm that all merge fields, which can be identified by the {{curly braces}}, match the available merge field list. If a new merge field is required, update the recipient list query with the appropriate field export or spreadsheet from the Edit recipient lists page.

To help avoid typos, click the merge fields listed in the Edit Message window to insert the merge field at the cursor location within the message

This warning may also appear if advanced liquid markup is used such as splitting missing checklist items and listing them using {{item}}, or using a forced value snippet.

"Warning: . . . in body is an unknown merge field"

This warning can occur under the following scenarios:

  1. Creating a variable/merge field using Liquid markup
  2. Using related event merge fields
  3. Using the "Form-Payment-Receipt" merge field
  4. A merge field does not exist

There are three methods for rectifying the third scenario:

  • Ignore the warning (e.g., in the case of using the "Form-Payment-Recipient" or related events merge fields)
  • Remove the merge field
  • Correct the merge field
  • Add the corresponding export to the recipient list
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