Via a setting you can restrict to only confirmed contacts, i.e. from double opt in.
This is useful if you are using double opt in for all your sign up processes. Sending to confirmed contacts only should result in better delivery and response rates.
To prevent sending to unconfirmed contacts select ‘ON’ for the Only Send to Confirmed Contacts setting in Settings > Contacts > Confirmed.
After the setting has been turned on, green (confirmed) text will appear next to confirmed contacts, and confirmed contacts will be the only ones that are added to campaigns when a group is selected.
To find the contacts who require confirmation click here.