Throttling is a feature that allows you to control the sending rate of an email campaign.
ISPs place rate limits on IPs or domains from their end based on IP/domain reputation and sending pattern of the marketers. Normally there is an upper limit for volumes originating from an IP. Throttling helps prevent exceeding these limits, which could result in deferrals/blocks/reputation drop, especially while sending high volume campaigns and/or scaling up the volume.
To create a campaign throttle, on Step 3 of Campaign creation, under Delivery Controls, select the Throttle time from the drop-down.
Note - The throttling time refers to the number of email batches (batch size of 100) to be delivered in the user-selected time duration.
For example, if a user selects 3 hours for a campaign with segment size of 18000 (i.e. 180 email batches of 100 emails each) then 1 batch (100 emails) will be delivered every minute for 3 hours (i.e. 180 minutes)