Inviting via Doodle lets you track who is still missing from your poll.
To use this feature you create a poll as usual and then check 'Only invited people can participate' on Step 4 of the poll wizard.
After sending out the invitations you can keep track of who is still missing on the admin tab by clicking 'Who is missing?' or on the poll table view also by clicking 'Who is missing?' above the participants list. The list is only available if you are a Premium Doodle user.
In the 'Who is missing'-view you can see who accessed the poll and when and also who is actually missing. Doodle also provides the option to contact the missing participants manually as well as to send reminders automatically.
Be aware that using this function you will have to invite additional participants again via Doodle (each participant receives a unique participation link). These links can only be used once and can therefore not be forwarded.
The invitation system can't be changed afterwards. If you want to receive a 'general' participation link, use 'Everyone with a link can participate'.