You can refer to CRM:0082139 for an example .csv file and an explanation of how this feature would have benefited me in a real situation.
Occasionally, I need to send an email to a group of managers with information about their employees. Sometimes, a manager has more than one employee that is being affected by a new program, so the manager is included multiple times in the .csv file that I am importing to PoliteMail.
Unfortunately, PoliteMail automatically removes duplicate email addresses from a .csv file upon import. As a result, I can't use PoliteMail to send these emails, we need to go back to mail merge technology.
It would be extraordinarily helpful if PoliteMail would provide an option during .csv file import to "keep duplicate email addresses" in the imported file.