Email throttling: three things it can mean, and which one is costing you
One word, three different problems. Sometimes you slow your own send on purpose. Sometimes Gmail slows you down. Sometimes your platform runs out of room.
- 132Throttling
- Controlling the rate at which emails are sent to avoid overwhelming servers or being flagged as spam.
- Done by you
- Gradual send in Klaviyo, which sends a campaign in batches
- Done to you
- A mailbox provider deferring mail it isn't ready to accept
- Klaviyo's own meaning
- Emails that couldn't go out in time because of volume limits
Who's throttling whom, and how to tell
| Who's doing it | What it looks like | What to do |
|---|---|---|
| You, on purpose | A campaign going out in batches over hours | Use it for unusually big sends |
| Gmail or another provider | Mail arriving late, then bouncing if it carries on | Slow down and send to the engaged |
| Klaviyo, on your plan | Recipients skipped on a huge send | Check limits and schedule early |
The first is a tool. The second is a warning. The third is admin, and it's the one that bites at Black Friday.
Gradual send: slowing a big campaign on purpose
Klaviyo's Gradual send sends a campaign in batches, a set share of the audience every hour or every minute. Klaviyo pitches it for pacing a send to support deliverability, and for avoiding a traffic spike on your site as people click through.
Use it when a send is far bigger than your normal volume, or when your site, stock or customer service can't take everyone at once. It won't run alongside an A/B test. And don't use it on a flash sale that ends tonight, because the last batch hears about it hours after the first.
When a mailbox provider defers your mail
Mailbox providers throttle too. When mail arrives faster than they trust you with, they accept some and tell the sending server to try the rest later. Your platform keeps retrying for a while, so it looks like a slow send. Keep pushing and the delays turn into bounces.
That's a reputation signal, not a technical fault. Google's sender guidelines ask for email at a consistent rate, without bursts, with volume growing slowly. So the fix is the dull one. Send to people who engage, and stop leaping from small sends to the whole list.
Klaviyo's version: the send that ran out of room
Klaviyo's help centre uses the word for emails that can't go out in the time available because of volume restrictions. Think of a campaign bigger than your plan allows, with flexible sending and auto-upgrade switched off, or a huge send scheduled with too little lead time.
The people it missed don't get the email. Klaviyo's fix is to resend to them, with everyone who did receive it excluded, so nobody gets it twice.
- Check your plan's sending limits before peak, not on the morning
- Schedule the biggest sends well ahead of send time
- Split a giant send by time zone, or into two audiences
Related terms
FAQs
Does sending in batches help deliverability?
It can, when a send is much bigger than your usual volume, because the mailbox providers see a steadier flow. It won't rescue a bad audience. Batch an unengaged list and you've just spread the same complaints across the afternoon.
Why did part of my campaign arrive hours late?
Check the send settings first. A gradual send, or sending in each recipient's local time zone, staggers delivery on purpose. If neither was on, a mailbox provider probably deferred some of it. When the late ones all sit at one provider, that points at your reputation there.
Should we throttle a flash sale email?
Usually not. A flash sale works because everyone hears at once, and batching hands the best stock to whoever landed in the first batch. Throttle it only if the audience is far bigger than your normal send, or your site and stock can't cope with the rush.
Rather we explained it on your own account?
Bring your Klaviyo account to a growth consultation. We'll walk through what this means for your numbers, in plain English, and what we'd fix first.
Half an hour with Theo, our founder.
We're all about relationships built on trust, mutual respect and a shared vision for success. If that sounds like your vibe, let's make some waves together 🌊
