Below follows an extensive review of the advanced functions when importing subscribers.
If this option is selected, suspended subscribers in the system will be reactivated. A subscriber is suspended once the system has received three bounce notifications from 3 subsequent newsletters. We advise not using this function.
Update subscriber data
If this option is selected the imported file will, if the receiver already exists, overwrite existing data fields in the system. Therefore, please be aware where you have the latest data stored if you need to update your subscriber list.
Ignore empty data values
If this option is selected all empty data values will be ignored. Thus the subscribers’ data will not be updated if a cell in the import file is empty.
This function is beneficial to use if there is a risk of duplicates in the import file and if there is data on some data fields where others are empty. If, for example, two similar email addresses appear and the upper has the data field "First name" filled and the lower data field has an empty cell in "First name", the system will overwrite the upper first name with an empty cell if one has not selected Ignore empty data values.
Unsubscribe other subscribers
Please contact firstname.lastname@example.org if you wish to unsubscribe subscribers in the import, as this function requires that you are absolutely certain of the outcome you wish to achieve.
For further information please se this comprehensive import guide