← All topicsDeliverability Overview › Throttling, Greylisting & Shaping
Accuracy / correctness · 2
accuracyaiSummary names Gmail and Outlook as example throttling providers; I deliberately did not name specific providers in narration (kept it 'the receiving server') to avoid implying named-provider behaviour as a benchmark. This is safe and matches the misleading-framings rule. No factual drift: 421/450 codes, 'deferred not rejected', volume-vs-reputation reasons, and the new-domain/IP-warmup trigger all match the article exactly.
accuracyArticle says 'usually over minutes or hours' for batch delivery. I preserved 'over minutes or hours' verbatim in meaning. No unhedged benchmark or invented number added anywhere. The '500,000 messages in an hour' figure is the article's own illustrative example, not stated as a real threshold.
Would elevate the video · 1
elevateThe article explicitly frames deferrals against BOTH a hard bounce (permanent failure) AND a block (outright rejection) as a three-way contrast. I kept all three (421/450 deferral vs 550 hard bounce vs block) in Beat 2 and the terminal cue. Confirm the visual actually shows the block state too, not just the hard bounce greyed out, so the full three-way distinction lands.
Considered, left out · 1
skipThe article's 'build sender reputation, clean list, fix authentication' fix paragraph names three separate Almanac links (IP warming, sender reputation, SPF-as-authentication). I compressed these into a single checklist takeaway plus two Concepts links rather than half-explaining each. Right call for a single-question video, the how-to-fix detail is its own video (002.009.006), linked.
What is email throttling, and why your mail arrives slowly
Question: 002.009.001 · What is email throttling? · ~2:45 · single-question video
COLD OPEN
You hit Send. Some land now. Some land tomorrow.

You hit Send. The messages go out. But they don't all arrive at once. A few land right away, some trickle in over hours, and a couple show up the next morning. That slow drip has a name, and it's not a bounce. It's throttling.

⬡ journey-flow, a burst of envelopes hits a gate; only a few pass at a time, the rest queue up behind it
BEAT 1, the one-line answer

Throttling is when the receiving mail server deliberately slows down how fast it accepts messages from your domain or IP. Your mail isn't rejected. It gets queued and delivered in smaller batches, usually over minutes or hours. The server is saying "I'll take these, just not all at once."

⬡ gauge-meter, an acceptance-rate needle eases back from full to a steady trickle, labelled "accepting, slowly"
BEAT 2, how to tell it's throttling and not something worse
Deferred, not dead.

Here's how you spot it. Your sending logs show deferred messages, often stamped with a "421 Try again later" or a "450 Requested mail action not taken." Those are temporary. That's the key difference. A hard bounce is a permanent no. A block is an outright rejection. A deferral just means "come back in a bit, we'll take it then."

⬡ terminal, log lines type out, a 421 and a 450 highlight in teal, a 550 hard bounce greys out beside them for contrast
BEAT 3, why it's happening to you

So why you? The most common reason is plain volume control. If Captain Kraken's shop suddenly fires off five hundred thousand messages in an hour, the server spreads that load out so it doesn't drown. But throttling is also a reputation signal. If a server doesn't recognize your IP or domain yet, or it's seen inconsistent behaviour from you before, it slow-walks your mail while it decides whether you're a legitimate sender.

⬡ split-compare, LEFT "Volume: 500k in an hour, spread out" vs RIGHT "Unknown sender: watched while evaluated"
SUBSCRIBE

If this is clearing things up, subscribe. We're working through every deliverability question, one at a time.

⬡ title-card, "Subscribe, the deliverability series"
BEAT 4, when it happens most

Throttling shows up most when you're sending to a brand new domain, warming up a fresh IP, or right after a spike in complaints or bounces. New senders warming an IP almost always hit some throttling. That's normal, providers are just getting used to seeing your traffic.

⬡ timeline, a warmup ramp over days, throttling heavy at the start and easing as the line climbs
TAKEAWAY

So the fix is almost always the same slow-and-steady work: build your sender reputation over time, keep your list clean so bounces and complaints stay low, and get your authentication set up right. Throttling usually sorts itself out as your reputation improves. If it gets worse instead of better, that's your signal something else is going on.

⬡ checklist, "Build reputation · Clean the list · Authenticate · Watch the trend"
NEXT / SUBSCRIBE

Want to know why providers bother slowing you down in the first place? That's the next video. Subscribe and it'll be waiting for you.

⬡ end-card, Subscribe + Next: "Why mailbox providers throttle" (002.009.002)
DESCRIPTION

What is email throttling? It's when a receiving mail server deliberately slows how fast it accepts messages from your domain or IP. Your mail isn't rejected, it's queued and delivered in smaller batches over minutes or hours. In this short: how to spot a deferral (those "421 Try again later" and "450" log lines), why it's different from a hard bounce or a block, the two main reasons providers do it (volume control and reputation evaluation), and why it hits new senders and IP warmups hardest.

The fix is rarely dramatic: build sender reputation over time, keep bounce and complaint rates low, and get authentication right. Throttling usually resolves as your reputation improves.

0:00 You hit Send, some land slow

0:15 What throttling actually is

0:40 Deferred, not dead (421 and 450)

1:10 Why it's happening to you

1:45 When it happens most

2:10 The fix

Concepts in this video:

IP warming → reviewmyemails.com/emailalmanac/sender-reputation/ip-reputation/what-is-ip-warming

Sender reputation → reviewmyemails.com/emailalmanac/sender-reputation/overview-and-fundamentals/what-is-sender-reputation

Next: Why do mailbox providers throttle emails? → [link 002.009.002]

Full written guide → reviewmyemails.com/emailalmanac/deliverability/throttling-greylisting-shaping/what-is-email-throttling

#email #deliverability #emailmarketing

CONNECTIONS
• next: 002.009.002 Why do mailbox providers throttle emails?
• related: 002.009.004 How does greylisting work?
• prerequisite: 002.003.001 What is sender reputation?
• vocab: throttling, deferral, 421, 450, hard bounce, IP warming, sender reputation