How to send confirmation when importing contributions
Confirmation sending can't directly from import.  There ARE ways to do it, but it slows down the import considerably, so I'd recommend doing it separately.  Here are your options:

Bulk confirmation


When importing, have an easy way to search for the contributions that were just imported.  Perhaps that's already possible because of your data.  If not, add a custom field "Needs confirmation" to your data, and populate that.
Using Find Contributions, find the contributions you just imported.
From the Actions menu, select Receipts - print or email and send confirmations as per the manual receipts documentation.



You could also use CiviRules, but as I started to document the process I realized how complicated that would be - I definitely think the bulk confirmation above is the way to go.