What Is Throttling?

Definition

Throttling is a way to control how many emails you send at once. In other words: it is all about pacing. Rather than doing an email blast, you send them out in smaller groups, one at a time. This slower pacing helps emails reach inboxes without triggering spam filters or overwhelming Internet Service Providers (ISPs).

Example

Let’s say you are running a large campaign with 10,000 emails. Do not send 10,000 emails at once. Instead, send only 1,000 per hour. This prevents overload and keeps your emails on a smoother delivery path. It also helps you avoid the spam folder, keeping your sender reputation intact.

Types of Throttling in Email Marketing

There are different ways to use throttling in email marketing. Here are a few common types:

• ISP Throttling. ISPs often set limits on how many emails they will accept. This is divided per sender within a certain period. If you happen to go over that limit, they may temporarily stop accepting emails from you. This kind of throttling keeps their systems running smoothly and prevents spam overload.
• Self-Imposed Throttling. Marketers sometimes set their own throttling limits. This lets them control how fast their emails go out. Slowing down the rate prevents large spikes in volume. This keeps emails from appearing spammy.
• Bounce-Back Throttling. Some email systems automatically reduce sending speed if they detect a high bounce rate. This kind of throttling helps you avoid issues with invalid addresses. You can pause to fix the list, and then continue the campaign without further problems.

Why Throttling Is Important

Throttling keeps your sender reputation healthy. ISPs and email providers watch your sending patterns, and sudden high-volume emails can raise red flags. Throttling shows that you are sending emails responsibly, pacing your messages in a controlled way. This approach builds trust and makes it less likely that ISPs block your messages.

Throttling also improves recipient engagement. When emails arrive in smaller waves, they are more likely to be seen and opened. A large flood of emails can easily get ignored, but smaller, spaced-out batches can lead to higher open rates. Even though it takes more time, throttling gives each email a better chance to reach the inbox and capture attention.

Remember that in email marketing, pacing matters. Throttling supports that pace, helping you build trust, keep good delivery rates, and reach more recipients.

Related terms

• Sender Score
• IP Warming
• Bounce Rate
• List Hygiene

Related articles

• How to Clean an Email List
• How to Reduce Bounce Rate
• Email Deliverability: 101 Guide