I did not receive a mail after donating!
Well that's strange. Are you sure it hasn't landed in your spam folder?
If your mailbox is full, you will not receive any new emails, including the donation mail. With gmail, you can see it at the bottom of the gmail.com webpage!
Wrong mail address
Do you have a wrong/outdated mail address you're using on PayPal? That's no problem. Just let me know at firstname.lastname@example.org what your new mail address is and proof, that you have actually donated. This could be the transaction ID or you could forward the mail you got from PayPal to the mail above!