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Just to check, say for example I have List A and List B. List A already contains firstname.lastname@example.org and list B contains email@example.com. When I import List C, which contains both firstname.lastname@example.org and email@example.com, will it suffice to say List C will not import these 2 emails?
Also, how does duplicates work across the different brands?
Brands are all independent of each other. Duplicates aren't de-conflicted across brands and lists.
However, duplicates will be de-conflicted in the same list. For example if you import firstname.lastname@example.org and email@example.com into List A, the next time you import these same email addresses into List A, they will not be imported. But if you import these 2 email addresses into another list, eg. List B, they will be imported.
If you're worried that when you send a campaign to both List A and List B and these two emails will get the same email twice, they won't. They will only receive the email once even though they appear in more than one list.
How about if I send to List A today, then I send the email to List B say two weeks later. Will they receive once or twice?
Then of course they will receive it twice.