It's not a good idea to email someone multiple times a day, or too many times in a week. Luckily, Marketo has communication limits to help.
When any person exceeds the set communication limits, Marketo blocks non-operational emails (operational emails always send).
1. Select your smart campaign and click the Schedule tab.
2. Open Qualification Rules and check the Block non-operational emails checkbox.
To make this the default, edit your communication limits in the Admin section.