Contribution receipt not being sent after paying with Paypal
Check the logs at /media/civicrm/ConfigAndLog shortly after a payment has been made but no confirmation sent.

You should see the payment Mar 15 19:13:18 [info] Contribution record updated successfully

Then you should see the contribution receipt. There may be an issue here e.g. 

Mar 15 19:13:18 [info] $Fatal Error Details = Array ( [message] => The requested Profile (gid=XXXXX) is disabled OR it is not configured to be used for 'Profile' listings in its Settings OR there is no Profile with that ID OR you do not have permission to access this profile. Please contact the site administrator if you need assistance. [code] => )

If you see something like the above, the issue is that Civi cannot access the information that was entered in the profile.