Why is my newsletter stuck in "Sending" or "Processing"?

This guide explains what each status actually means, how the progress numbers work, and when something has gone wrong. For the full status list, see What Do Letterhead Statuses Mean?

What “Processing” and “Sending” mean

Every letter moves through a fixed set of statuses on its way out the door. The two you’re most likely to see right after scheduling are:

• Processing — Letterhead has handed your letter off to the email service provider (ESP) and is creating the campaign on their side. No emails have left yet.
• Sending — The campaign has started delivering. As delivery progresses, the status updates to Sending (25%), Sending (50%), and Sending (75%). At 100%, the status flips to Published.

A normal send looks like: Scheduled → Processing → Sending → Sending (25%) → Sending (50%) → Sending (75%) → Published.

The percentages reflect delivery progress and update on a polling schedule — typically every few minutes — so the bar ticks up in chunks rather than smoothly.

How long should it take?

• Under 5,000 recipients: Processing finishes in seconds; Sending → Published completes within a minute or two.
• 5,000–50,000 recipients: a few minutes, mostly ESP delivery time.
• 50,000+ recipients: can legitimately take 10–30 minutes or longer on shared ESP infrastructure.

Well past those windows with no movement? Work through the causes below.

Cause 1: It’s normal — the percentage hasn’t crossed the next threshold

The Sending percentage advances in threshold jumps, not smoothly. If you’re at Sending (25%) for a few minutes, open the letter’s metrics view (click the letter in the channel’s Emails list). If the Sent count is climbing, the send is working — the status just hasn’t refreshed.

What to do: refresh after a few minutes; if Sent keeps growing, leave it alone.

Cause 2: Stuck on Processing for more than 5 minutes

If Processing never moves to Sending, campaign creation on the ESP side has stalled or errored. Common reasons:

• The ESP rejected the campaign — most often invalid or expired ESP API credentials, especially if a key was rotated mid-flight.
• A curation source timed out while Letterhead assembled the content.
• The rendered HTML is too large to deliver (large embedded images, very long curation lists).

What to do:

1. Open the letter’s metrics view. If Sent is zero and unchanging, the send hasn’t started.
2. Check the letter’s content check on the preview step — an Email Weight warning means the letter may be too heavy for the ESP.
3. After 15+ minutes on Processing, contact support with the letter’s Unique ID and channel slug so the team can check the job logs and retry.

Cause 3: Stuck on the same Sending percentage

• Delivery actually slowed — ESPs throttle large sends or after bounce spikes.
• The status-update process is delayed — a background task polls delivery metrics; if it’s backed up, the label lags the real state.
• The ESP errored mid-send — rare; usually shows up as a rapidly climbing Bounce count.

What to do:

1. Check Sent, Delivered, Bounces, and Opens in the metrics view. If Sent is at or near your audience size, the send is done and only the label is behind — wait or refresh.
2. If Sent is well below audience size and not growing, contact support.
3. If Bounces are spiking, that deserves its own look — some ESPs auto-pause sends at high bounce rates.

Cause 4: Scheduled time passed but status is still Scheduled

The letter didn’t get picked up by the scheduling worker — rare, but possible during deploys or backend incidents.

What to do: on the letter’s schedule step, set the Date and Time to a minute or two in the future and re-save. The send should pick up on the next worker cycle.

Cause 5: A/B test “pick the winner” hasn’t fired yet

If your letter is an A/B test that auto-picks a winner, you’ll briefly see Processing again at the pick-winner step before the main send begins. This is expected — it usually takes 5–15 minutes depending on test settings.

What you can’t do once a send is in motion

• Cancel from the UI — once past Scheduled, the campaign is on the ESP side. If you must halt one, contact support immediately.
• Reorder recipients — delivery order is controlled by the ESP.
• Edit the letter mid-send — content was rendered at the start of Processing; later edits won’t affect what’s delivering.

Still stuck?

If a letter has been on Processing or Sending without progress for more than 30 minutes:

1. Note the letter’s Unique ID (in the channel’s Emails list), the channel slug, and the scheduled time.
2. Screenshot the metrics view showing Sent / Delivered / Bounces.
3. Contact support with that information — the team can check the job queue and the ESP campaign, retry the status update, or escalate.