Understanding email throttling

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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: 

  • The auto-upgrade feature is disabled and a campaign exceeds your plans 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 (>1,000,000) of recipients and many included and excluded lists/segments. 
    • More recipients were calculated at send time than at scheduling time.

If Klaviyo can tell at the time of scheduling that your campaign will be throttled (e.g., if it will exceed your plan limits), you’ll receive an in-app warning and won’t be able to schedule the campaign. However, if it’s not clear in advance that your campaign will be throttled (e.g., if additional sends between your campaign’s scheduling and send time push you over your plan’s limits), your message will be throttled.

Best practices to avoid throttling

To avoid throttling, we recommend these best practices: 

  • Enable auto-upgrade for your email plan, so your billing plan can automatically update if needed 
  • For every 1,000,000 email recipients in a given campaign, add an hour between when you schedule the campaign and when it should send (i.e., if you are sending to 3,000,000 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)
  • The “send now” functionality is not recommended for time-sensitive sends with >1,000,000 recipients because 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. 

  1. Click Audience > Lists & Segments in the Klaviyo navigation sidebar
  2. Click Create List / Segment
  3. Select Segment
  4. Create a segment with 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]
    A segment of everyone who received the throttled campaign

  5. Click Save Segment
  6. Click Campaigns in the Klaviyo navigation sidebar
  7. Click the three dots icon next to your throttled campaign 
  8. Click Clone
    The Clone button for a Klaviyo campaign

  9. In the Send to field of the new campaign, add the same list(s) and segment(s) used for the original campaign
  10. In the Don’t send to field, add the segment of message recipients you just created 
  11. Proceed through the steps to schedule and send your campaign 

Outcome

When you resend a campaign but skip a segment of profiles who have already received it, you can be certain that your subscribers will not receive the same message twice. By following the steps outlined above, you can send your message to those who were skipped when it was throttled. 

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