To import the birthdays of your contacts, you have to create and import an Excel file with the parameter (column name) "birthday". The name definitely has to be "birthday" so that the system will be able to read the column data automatically as birthdays. Additionally, the column format has to be text (not date or number).
To change the column format to text, right click on the letter of your birthday column. Choose from the menu that appears "Format cells".
After that, click in the formatting window on the option "Text" and then "OK".
Write the birthdays with the following format: YYYY-MM-DD, for example 2016-09-26.
After that, save the file (we recommend to save in .xls or .csv format) and upload it like any other normal contact list (you can also check the Importing contacts user manual).
Tip! If you have contacts' birthdays in your database, you can create an autoresponder that sends them happy birthday wishes or birthday coupons. Read more from the manual Creating a birthday autoresponder.