Contents:
What is the Frequency Cap?
The frequency cap is the maximum number of emails that a contact can receive within the specified time period. If this limit is reached, the contact will receive no more emails and will be displayed in the Results Summary page as Frequency cap.
How does it work?
When a launch list is generated, the frequency cap checks each contact and sees how many emails they have been sent in the last n days. Those who have reached their limit are removed.
If an email campaign launch is spread over more than one calendar day, either due to versions being so scheduled or due to it being launched close to midnight, the frequency cap will think that each contact in the launch list received the campaign on both days. This can lead to contacts reaching their maximum limit sooner than expected.
If you use Send Time Optimization, the Frequency Cap will apply to each child campaign at the moment of launch.
Activating the frequency cap
To turn this feature on, go to the Admin menu and select Frequency Cap.
Then activate the check box and set the number of emails (max. 5) and the length of the time period (max. 7 days).

When the frequency cap is activated, all emails will check their launch lists for contacts who have reached their limit and remove them.
Which email types count towards the cap?
All email types except transactional (event-triggered) emails will add to the frequency count for each contact, regardless of whether they opened them or not.
Event-triggered (transactional) emails do not add to the frequency count. That is, contacts can receive these emails without affecting their ability to receive other mails.
Which email types are affected by the cap?
Although transactional mails do not increase the frequency count, when the limit is reached, all types of email are affected, that is, contacts will not receive any emails of any sort after that. To this end, if you want to be sure that critical emails (e.g. your transactional mails) are still delivered, you can activate the Ignore frequency cap for individual campaigns in the option with these on the Email Settings page.
This option only appears if the frequency cap is turned on. All contacts in the launch list will be sent this email regardless of their frequency count.
Additionally, campaigns with this checkbox activated will not count towards the frequency cap and therefore will not affect any other campaigns.

What happens to the contacts that are excluded?
Those contacts who have already been sent the maximum in the last n days are excluded from the launch list and are listed under Frequency cap in the table of Number of emails not sent on the Results Summary tab of the email reporting.