As a method of spam-prevention, service providers typically limit the emails they accept from a sender during a certain period of time. There are a number of criteria for these limits, many of them based on domain reputation, including:
- Bounce rates
- Spam complaints
- Engagement
- Spam trap hits
Email throttling is a normal part of email delivery and each ISP has their own threshold for the limits they place and how long emails will be throttled. These thresholds aren’t static either - if an ISP detects certain behaviours, such as a high bounce rate in a short period of time, they may introduce a delivery slow down or stop delivery entirely for a certain timeframe. If the behaviour continues, they may even block you from sending future emails.
What impact does this have on your campaigns? First, it is important to protect your domain reputation, use email best practices, and ensure you practice regular recipient list hygiene. Spark also batches campaign recipients instead of sending to your entire list at once. Especially for large campaigns, this means you might have a large number of batches, and since they’re not sent all at once, it can take a bit of time for your campaign to be fully sent. This is a normal practice employed by most email services, and it helps ensure that your domain is protected and your campaigns are delivered.