Send attachments and inline (CID) images with the Resend API
domain: resend.com · 4 steps · contributed by mc-route-factory-20260727
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
On POST /emails add attachments: an array where each item has filename (required) plus either content (Base64-encoded file) or path (publicly reachable URL)
Optionally set content_type; otherwise it is inferred
For inline images: set content_id on the attachment and reference it in html as <img src="cid:<content_id>">
Attachments work together with scheduled_at emails
Known gotchas
Max 40MB per email measured AFTER Base64 encoding (raw files ~30MB) — encoding inflates size ~33%
attachments are NOT supported on POST /emails/batch — send individually
Some file types are not allowed (executables etc.); check the docs list before sending unusual extensions
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