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.

On a channel sending through Letterhead’s own email connection, the newsletters list shows these steps as a live progress meter and updates itself roughly once a minute — you don’t need to refresh the page to watch it move. A channel sending through a connected ESP (Iterable, Braze, and similar) instead shows a plain Sending badge for the whole send, since that ESP doesn’t report delivery progress back to us; check that ESP’s own dashboard for real-time counts.

The percentages reflect delivery progress, not how much of the list has simply been handed off, and they advance in the fixed jumps above rather than a smooth animation.

”Waiting for initial metrics” right after Published

Once a Letterhead-connected send finishes delivering, it doesn’t always flip straight to a plain Published badge on the list. If reporting hasn’t caught up yet, the row shows Waiting for initial metrics in its place instead — this is expected, not a failed send, and it clears itself the moment reporting catches up, usually within a minute. This state never lasts more than about three hours; past that, the row falls back to an ordinary Published badge whether or not metrics have actually landed. If you open the letter’s metrics view well after that window and still see zero opens and clicks, that’s a reporting problem — contact support with the letter’s Unique ID.

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 on a Letterhead-connected channel, the list will update itself within about a minute once the next threshold is crossed — no refresh needed. If it’s been longer than that with no movement, open the letter’s metrics view (click the letter in the channel’s Emails list); if the Sent count is climbing there, the send is working and the badge will catch up shortly.

What to do: wait a minute or two and let the list update itself; if Sent keeps growing in the metrics view, 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 — it’ll catch up on its next automatic update.
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 is testing, picking a winner, or sending it

An A/B test shows its own progress on the list instead of a plain A/B Testing badge, in order:

1. Testing — winner picked in ~N min — the two subject lines are out to the test group; the countdown runs down to the one-hour mark when a winner is chosen. Queue timing can make the estimate run out a minute or two early — that’s expected, and it never shows a negative or stale number.
2. Picking the winner… — the countdown has reached zero and Letterhead is tallying opens to choose the winning subject line. This is normally quick, but can take a couple of minutes if the countdown ran out early.
3. Waiting for initial metrics — you may briefly see this again right as the winner’s send starts, before its own delivery numbers begin reporting — the same state described above for an ordinary send.
4. Sending the winner — the winning subject line is going out to the rest of your audience, with the same live delivery meter as an ordinary Letterhead-connected send.

From there it behaves like any other send — a plain Published badge once delivery is confirmed. The testing phase itself takes about an hour; how long the winner’s own send takes on top of that follows the same timing as any other send (see “How long should it take?” above).

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.