Understand a failed send Live

The difference between sent and delivered, where failures show up, and the most common causes for email and SMS.

Updated 2 min readMaintained by Landing Zone

"Sent" and "delivered" are not the same thing. Sent means Landing Zone dispatched the message; delivered means the receiving mail server or carrier network accepted it. A message can be sent and still never reach the contact — and some contacts are excluded before anything is sent at all. This guide walks you through telling those cases apart.

Before you start

  • A batch that finished with fewer delivered messages than you expected.
  • Access to Batches, where per-send results live.

Steps

  1. Open the batch drill-down. Go to Batches and open the batch in question — that's where its results and failures appear, including opens, bounces, replies, and opt-outs for email.
  2. Separate exclusions from failures. Exclusions happen before the send: the preview removes contacts for reasons like consent not verified, the 30-day cooldown, suppression matches, line type, and quiet hours (SMS). Excluded contacts were never sent to — that's the eligibility pipeline working, not a failure.
  3. Compare delivered against sent. For the messages that did go out, the gap between sent and delivered is your delivery problem to diagnose.
  4. Diagnose email failures. The common causes are bounces — invalid or dead addresses — and a sending account that isn't properly connected or verified. Clean addresses with email verification and work through Email delivery issues.
  5. Diagnose SMS failures. The common causes are an A2P 10DLC registration that isn't approved yet (sending gates on approved status — see the A2P 10DLC setup guide), non-mobile line types, and carrier filtering. Work through SMS delivery issues.
  6. Fix the cause, then send again to a cleaned audience. Verify addresses and phone numbers, resolve account or registration problems, and build the next batch from contacts that can actually receive it.

Limitations

  • Delivery is ultimately decided by mail servers and carriers, not by Landing Zone — no platform can guarantee delivery.
  • Pre-send exclusions are by design. Contacts removed for consent, cooldown, suppression, line type, or quiet-hours reasons are shown in the preview's exclusion counts, not reported as failed sends.
  • Already-sent messages can't be recalled; fixing a cause helps the next send, not the last one.