After applying the 7.10.1 update, the Email Marketer tool may send repeated copies of an email.

The Email Marketer underlying code and logic was re-factored in 7.10. Additional logic is required to account for an unbound query for date criteria in the automation task.

Please apply the 7.10.2 Maintenance Release via the Utilities > Update WHMCS page.

A hotfix has been created for 7.10.1 only which will resolve the cause of this error:

https://whmcs.community/files/file/130-core-14565-prevent-repeated-emails-sent-by-a-single-email-marketer-rule/