Can the email receipt that I received in my mail box be used as a proof for warranty?

Hello, I have purchased a pair of Bose QC20i earphones from the Apple retail store at Fairview Mall, Toronto. However I noticed that the gentleman at the store did not print me a purchase receipt after I paid cash, I noticed this when I woke up this morning. The apple retail store at fairview mall did send me a copy of email invoice yesterday. So i'm wandering, if one day I need to get the warranty service (within one year). Should i use the email invoice as a proof that I did purchase the product? Will they still provide me the service if I show them the email invoice? Other wise what should I do to prove that I did purchase the product? PS: I do not have a credit history since I purchased by CASH.