# Email Throttling & Rate Limits — What's the Difference

> Throttle, rate limit, sending limit. Different words, often confused. This guide separates them plainly — who enforces each — and shows the one control you actually set in AcelleMail: the per-server Sending limit.

- Canonical URL: https://acellesend.com/kb/articles/email-throttling-and-rate-limits-explained
- Author: Lena Hart, Email Deliverability Editor
- Category: Sending & Deliverability — SMTP setup, bounce handling, sender reputation, IP warmup, throttling
- Content type: tutorial · Difficulty: beginner
- Tags: Acellemail
- Published: 2026-05-16 · Last updated: 2026-08-15
- Reading time: 5 min
- Publisher: AcelleMail Knowledge Base, https://acellesend.com/kb

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## What this is for

You've heard "throttle," "rate limit," and "sending limit" used like they mean the same thing. They don't. Two are something you set; the rest are decided by other people's servers. This guide draws the line clearly, then shows you the one control you actually have in AcelleMail — the per-sending-server **Sending limit**.

## The two words people mix up

**Throttle** is *your* side. You decide to pace how fast AcelleMail hands messages to a sending server — say, no more than 1,000 emails an hour. It's a voluntary cap you set. If you hit it, the rest of your campaign simply waits in the queue and goes out as the window rolls forward. Nothing fails; it just spreads over time.

**Rate limit** is *their* side. The receiving mailbox provider (Gmail, Yahoo, a corporate mail server) decides how much mail it will take from you in a given window. You don't set this and you can't see the exact number — it's the provider's call, often tied to your reputation. When you bump into it, the receiving server temporarily defers your mail with a "try again later" style response, and AcelleMail retries on its normal schedule.

The short version:

| Term | Who sets it | What happens when you hit it |
|---|---|---|
| **Throttle** (you, in AcelleMail) | You | Remaining mail queues, then sends in the next window — no failure |
| **Rate limit** (the receiver) | Gmail / Yahoo / the recipient's mail server | Receiver defers with a temporary "try later" response; AcelleMail retries |

Everything else you might have read — vendor daily caps, per-domain throttling scripts — is either your email vendor's own contract limit (you manage that in *your vendor's* dashboard, not in AcelleMail) or behaviour on the receiving side that no email tool controls. The only knob that lives inside AcelleMail is the throttle, and it's called the **Sending limit**.

## The one control you set: Sending limit

The Sending limit is set per sending server. Two servers can have two different limits — handy when you run a fast transactional server and a paced marketing one.

### Open the sending-server detail

In AcelleMail's sidebar, click **Sending → Sending servers**. The list shows every server connected to this account, with its **Sending limit**, **Status**, and **Created** date:

![Customer sending-server list](https://acellesend.com/plugins/acelle/landing/images/help/kb/sending-servers/01-customer-server-list.png)

The **Sending limit** column tells you each server's current cap at a glance — for example `1,000 / hour`, or `Unlimited` if no cap is set. Click the server name to open its detail page.

![Server detail — Connection + Configuration](https://acellesend.com/plugins/acelle/landing/images/help/kb/sending-servers/02-server-detail-full.png)

### Set the limit

On the server's detail page, find the **Configuration** card and the **Sending limit** dropdown. It offers a short list of presets:

- **Unlimited** — no pacing; AcelleMail sends as fast as the server accepts
- **100 emails per 1 minute**
- **1,000 emails per 1 hour**
- **10,000 emails per 1 day**
- **Custom** — pick your own number and window

Choose **Custom** and three more fields appear: **Per** (the count), **Every** (how many time units), and **Unit** (Minute / Hour / Day). So "5,000 every 2 hours" is Per `5000`, Every `2`, Unit `Hour`. Click **Save configuration**.

That's the whole feature. AcelleMail enforces the cap for that server — when the rolling-window count reaches your number, the queue holds the rest until the window slides forward. You don't add anything to your campaigns; you set it once on the server.

## When to set a limit (and when not to)

| Situation | Set a Sending limit? |
|---|---|
| Warming a brand-new IP or domain | **Yes** — start low and raise it over days |
| Established server, steady volume | Optional — leave it Unlimited, or set a cap as a safety brake |
| Big one-off campaign blast | **Yes** — pace it so you don't dump everything in one spike |
| Transactional / password-reset server | **No** — those need to go out immediately; leave it Unlimited |
| Several servers sharing the load | **Yes** — a per-server cap divides the volume across them |

A limit that's too low just makes campaigns crawl for no reason. A limit that's sensible protects a young IP and smooths out spikes. Match the number to what you actually send, not to a number that "feels safe."

## Common issues

| What you see | What it means | What to do |
|---|---|---|
| A campaign sends far slower than expected | The server's Sending limit is set low | Open the server → **Configuration** → raise the **Sending limit** (or set it to Unlimited) |
| Sends pause, then resume in bursts | Normal — the rolling window filled up, then reset | Nothing to fix; raise the limit only if the pace is too slow for you |
| Mail to one provider keeps getting deferred and retried | That receiver is rate-limiting you (their side, not yours) | This isn't a Sending limit problem — see the deliverability guides below; check bounces and reputation |
| The Sending limit column shows `Unlimited` and you wanted a cap | No limit was ever set on that server | Set one via the Configuration card and **Save configuration** |

## What to do after

- Decide whether each of your servers should be capped or Unlimited, and set them in **Sending → Sending servers**.
- If deferrals are coming from the receiving side, work the deliverability angle instead — start with bounce decoding and an incident runbook.
- Spreading volume across more than one server? See the multi-server guides below.

## Related articles

- [Sending throttling strategies](https://acellesend.com/kb/articles/sending-throttling-strategies)
- [Configuring multiple sending servers](https://acellesend.com/kb/articles/configuring-multiple-sending-servers)
- [SES sending limits cookbook](https://acellesend.com/kb/articles/ses-sending-limits-cookbook)
- [Multi-server rotation pattern](https://acellesend.com/kb/articles/multi-server-rotation-pattern)

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