No the e-Marketing service has an automatic de-dupe function on the system so if you add new contacts to a tag group and send out the campaign again, it will not go to contacts who have been sent the campaign.
What is the De-dupe for?
The de-dupe prevents you sending out the same campaign multiple times to the same email address.
It is set as checked by default to ensure this does not happen.
If you un-check the box then if you send out the campaign to other tag groups that may include the same contact then the recipient will receive the email campaign again which is not advisable as this will be seen as spamming! Always leave the box ticked on default.
Please make sure you leave the DEDUPE box ticked as shown below:
