We often get asked if Campaign Monitor checks for duplicates when importing subscribers, so we thought we’d cover it here once and for all. The short answer, yes. We never allow duplicate emails to be imported into the same list and if someone tries to subscribe to a list that they already belong to, they won’t be added again.
This way a recipient will never get the same campaign twice and you’ll never be charged for sending the same thing twice. Even if a recipient is a member of two lists and you send a campaign to both lists, they’ll still only receive one version.