Maximum recipients at a contact level for each Campaign version can be limited by enabling the Set maximum send volume toggle under Content & Audience tab. Each version can have a different maximum volume limit. The campaign version will be sent to eligible recipients, and once the maximum volume has been reached, sending will be stopped, and the rest of the audience will not receive the campaign.
In computing the maximum volume, seed lists and control groups are not added to the count while seed counts are considered.
Maximum Send Volume Limitations
Right now, no message-skipped events will be queued to the recipients that did not receive the campaign because of the volume limit. Also, this feature will not be available when A/B testing is enabled.