Understanding email throttling

You will learn

Learn how and when Klaviyo throttles email campaigns, best practices to avoid throttling, and what to do if your campaign is throttled.

About email throttling

Email throttling refers to when some emails cannot be sent in a given time period due to volume restrictions. Klaviyo may occasionally throttle emails for one of the following reasons:

• Auto-upgrade and flexible overages are disabled and a campaign exceeds your plan’s limits.
• There are an unexpectedly high number of recipients and not enough time to send your email to all of them. This can happen when:
  • The final recipient count is not known until after a campaign is scheduled. This can happen in rare cases for campaigns with a high volume (e.g., more than a million) of recipients and many included and excluded lists/segments.
  • More recipients were calculated at send time than at scheduling time.

If Klaviyo detects at scheduling that your campaign exceeds your plan limits and your account cannot send beyond those limits, you receive an in-app warning and cannot schedule the campaign.

However, the warning might not appear if, for example, many profiles were added between when the campaign was scheduled and the actual send time.

Best practices to avoid throttling

To avoid throttling, we recommend these best practices:

• Choose flexible overages or auto-upgrade for your paid email plan. Flexible overages add sending capacity for a 1-time fee without changing your base plan. Auto-upgrade moves you to a higher plan tier.
• For every 1 million email recipients in a given campaign, add an hour between when you schedule the campaign and when it should send (e.g., if you are sending to 3 million recipients and want your message to send at 4 p.m., go through the scheduling steps at or before 1 p.m.).
• For particularly large sends, consider breaking the send up (e.g., send by recipient time zone or split your list in two).
• Avoid using the “send now” functionality for time-sensitive sends with a million or more recipients.
  • The process of preparing a message to send to a list of this size may take multiple hours.

Email content does not impact whether or not your message will be throttled.

What to do if your campaign is throttled

If your campaign is throttled, you can manually resend the email to skipped recipients. If your campaign was throttled due to your email plan size, upgrade your plan before taking these steps.

The resend uses the membership of your selected lists and segments when its recipients are determined. It can include people who joined those audiences after the original campaign, as well as people who were skipped.

1. Click Audience > Lists & segments in the Klaviyo navigation sidebar.
2. Click Create.
3. Select Segment.
4. If the Create segment panel opens, enter a name and click Create segment to open the builder. Otherwise, enter a name in the builder.
5. Create a segment of people who received the original campaign using the following definition:
   • What someone has done (or not done) > Received Email > At least once over all time > where Campaign Name = [your campaign’s name]
     

6. Click Create segment.
7. Click Campaigns in the Klaviyo navigation sidebar.
8. Click the 3 dots icon next to your throttled campaign.
9. Click Clone.
   
10. Enter a campaign name and select a Send date. If Type is shown, keep Single channel selected. If account options are shown, choose Clone to the current account.
11. Click Clone campaign.
12. In the Send to field of the new campaign, confirm that the same list(s) and segment(s) used for the original campaign are selected.
13. In the Don't send to field, keep any lists and segments excluded from the original campaign and add the segment of message recipients you just created.
14. Review the campaign’s content and sending settings, then follow the steps to schedule and send your campaign.

Outcome

The cloned campaign targets eligible profiles in your selected lists and segments while excluding the segment of people who received the original campaign.

Additional resources