When a donor gives, by default, they will receive a donation receipt via email each time they give. This feature can be turned off in the dashboard. The receipt that we send out is for the donor's personal records and should not be used as an official tax receipt.
If you would rather send your own receipts, you can simply disable the donor receipt feature under My Account > Settings > Edit (found in menu button in the top right corner) > (uncheck) Email Donation Receipt to Donors.