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Preflight is a validation step that runs automatically when you attempt to send or schedule a campaign. It checks that everything required for a successful delivery is in place. Some issues block sending entirely; others surface as warnings that you should review but that do not stop the send.

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What preflight checks

The sender email address on your campaign must be verified in your workspace. Unverified senders cannot be used for delivery. Verify your sending domains and addresses in Settings → Senders.Blocking: Yes — an unverified sender prevents the campaign from being sent.
Your campaign must have a recipient audience or segment chosen. A campaign without recipients cannot be delivered.Blocking: Yes.
The subject line must not be empty. An email with no subject line is likely to be filtered or ignored.Blocking: Yes.
The campaign body must not be empty. A campaign with no content cannot be sent.Blocking: Yes.
Preflight checks that images referenced in your campaign are loading correctly. Images that return errors will appear as broken in recipients’ inboxes.Blocking: Warning — image issues are flagged for review.
Your workspace must have sufficient send credits or be within your plan’s sending limits to deliver the campaign. If you are at or over your limit, the send is blocked.Blocking: Yes if over limit.

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Fixing preflight issues

When preflight surfaces an issue, it links directly to the setting or section you need to fix. Resolve each blocking issue before attempting to send again. Address warnings even if they do not block the send — they indicate potential delivery or rendering problems.
1

Review the preflight report

Read each flagged item and note whether it is blocking or a warning.
2

Fix blocking issues first

Resolve any issues marked as blocking — these prevent the campaign from being sent at all.
3

Address warnings

Review and fix warnings where possible before proceeding.
4

Re-run preflight

After making changes, return to the send or schedule flow to re-run preflight and confirm all blocking issues are resolved.
Passing preflight means SendWhale has accepted your campaign for delivery and all required fields are present. It does not guarantee inbox placement — factors such as your sender reputation, content, and recipient engagement also affect deliverability.