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The Rule Engine supports account-level placement exclusions. This means that, based on the performance data of placements aggregated at the account level, you can exclude placements from an account.
Note: Excluding from an account means excluding from all the campaigns.
Why use it?
Excluding placements from an account helps prevent your ads from showing up on certain placements on the Display network or YouTube, overriding any campaign-level placement targeting.
For some cases, as with Smart Shopping and Smart Display campaigns, account-level placement exclusions are a great solution, as Google doesn't support excluding placements through a negative list or by excluding them at the ad group level.
You can read more about how account-level placement exclusions work here.
As detailed in Google's support page, you can enter a maximum of 20,000 placement exclusions at a time, and a total of 65,000 placement exclusions per account.
Please note that any URL associated with a Google domain (for example, youtube.com and mail.google.com) can't be added as placement exclusions.